OK, Kawboy, this may be a bit long to try to be clear in what I am talking about, so it won't fit in a PM.
In the drawing, the basic idea is to machine off the original cam gear down to diameter "D". That diameter, "D", is determined by bisecting the bolt holes in the new gear. Then machine the I.D. of the web of the new gear to match that diameter "D", plus maybe a half thou'. Of course, I'm talking in inches here, not metric! By opening up the I.D. of the new gear to match the turned down cam gear, the new gear should be able to clear the cam lobes. If not quite yet, then one of those "trapezoid" openings can be opened up a tiny bit to give the needed clearance without affecting the fit of anything. Of course, it's opposite (180 degree) matching opening must be machined to match it for balance.
OK, now we have the new gear placed around what's left of the original cam gear's web (now called the "cam web"). BTW, both webs also need to be matched in thickness with clean, flat surfaces.
Although the new gear has those odd trapezoid shapes, once the I.D. ("D") is machined wider, there will still be plenty of the web in contact with the cam gear's web. Not full circle, but still plenty.
Now you will have the new gear with it's two original bolt holes cut in half (the bolt holes, not the gear!!!).
To keep this new gear in place, you will need to machine two sandwich rings. The O.D. of these rings should fit snugly under the "shoulder" supporting the gear's teeth. This will keep it perfectly concentric with the gear to help maintain balance. These rings will have AT LEAST two bolt holes to do the clamping, but I would recommend adding two more so you have a bolt every 90 degrees. I only drew two holes in the drawing. Yes, the two new bolts will be passing through two of the trapezoid openings (possibly the two needing to be machined out a bit to fit over cam lobes!!!), but all that these bolts are for is to give added strength to the clamping force of the rings in the first place. The original two bolts will be used to create the adjustable cam timing.
These sandwich rings also will need a VERY shallow groove ("G") machined in their faces. Maybe five to ten thousands deep. The width of that groove should be maybe .050" wide and centered over the joint at "D". I won't go into the engineering why's and wherefores of this groove, but it is important. Both rings need this groove to face inwards toward the web surfaces. In my drawing I exaggerated the groove's size to help illustrate it's existence. It shouldn't be as wide or deep as the drawing makes it look like.
OK, now for the timing grooves in the cam.
The new gear's web has been machined with a wider I.D., hopefully bisecting the original bolt holes. New "half-holes" will need to be machined into the edge of the cam web now. Actually, here's where the adjustability comes in. To be able to rotate the cam for perfect timing, these two bolt holes need to be machined as half-grooves (see the figure in the middle left). Again, I exaggerated their size for illustration purposes. In reality they only need to be very short grooves. I'm sure that perfect timing will happen with very few degrees of shift needed. Maybe the equivalent of five degrees each way? Maybe allow a half-bolt-diameter shift each way.
Well, that's the concept. Web thicknesses don't need to be compromised as they would if you tried to keep full diameter webs and just thinned them out to get the teeth aligned correctly. In fact, adding these two sandwich rings will strengthen the whole assembly, especially using four bolts instead of two.
Back in the late '70's I built a Honda GL1000 engine to put out just under 200hp, and to fine tune the Norris cams to do that, this is basically how I made up adjustable cam "gears". I had to buy two new gears to be able to machine all four to fit precisely together.
Wow Bruce, you put a lot of thought into this. My only concern was removing the core of the gears since the gears are hardened through and through to to a very hard Rockwell. Stripped the teeth of a Nicholson file in one stroke. If they're that tough the gears could crack at the teeth from shock from the drive. The supporting rings you suggest would reinforce the gears. I like the idea. Like I said, I haven't given up on this mod. Still thinking about how I'm going to attempt this. A failure in the system could cost me a lot including an engine if the gears shatter and fall in to the pit.
I expected the new gear would be hardened. The only machining would be to open the I.D. up to spec, and POSSIBLY to open up two of the trapezoid openings, and that would all be done on a lathe using a grinder. I made up a holder to use my Dremel on my lathe for such precise work and for when I also have hardened materials that need "re-dimensioning".
The camshaft material should be a good grade of harder cast, so it should be machinable using carbide-tipped tooling.
My only concern is that if the new gear's web thickness is MORE than the cam's web thickness, it will be hard to thin it down by grinding. BUT, then maybe those clamp rings can be machined to accommodate the differences in web thicknesses.
You mentioned other aftermarket gears from other makers. Got any pictures of them and info on materials used?
Here's another really wild card for you to consider. Some cam grinding shops do a lot of experimental work for one-off racing engines and are good at completely re-profiling a cam, like for offshore boat engines that use one reverse direction engine. Kay Sissel used to cut up a Chevy head and a Ford head and use the intake valve section from the Chevy and the exhaust section from the Ford to TEDIOUSLY make up a whole new hybrid head. The valve spacing was then changed so he had cam lobes completely moved sideways on his custom cams to work right. Anything can be done if you find the right shop with a good man. A good shop could easily make up a new flange to fit your new gear and then weld that flange onto your cam shaft just offset enough that you wouldn't have to machine that new gear at all, except to give lobe clearance when slipping it on.
Lots of possibilities and ways to skin this cat! Easy? Not at all, but a lot of fun! And, as for messing up the whole engine if something fails, then leave the thing alone as it is and enjoy the stock ride. If all you do is create a way to fine tune the cam's timing with no other mods to take advantage of that, you probably won't feel any difference in the power anyway. I would be anxious to see what a 3-4 degree timing advance could do for upper power band shift. This could really benefit anybody racing these engines.
Oh what I could do with a lathe, a mill and an indexing head !! I could have so much fun. Camshaft development and valve spring development in the last 35 years has come a long ways. Beehive springs with oval wire - one could lighten up on the spring pressure and still reduce the spring harmonics, or raise the valve duration and lift while maintaining the same spring pressure. titanium retainers. Faster acting cam lobes......... I could create a list...... I really need to tool up.