There is no problem and the clamps work perfect. The brake force from the shoe in directed downward through the rubber pads. That thing has rubber cushioned brakes. The peddle force goes through the wheel bearing and frame. The clamps really don't do much. Now if you stabbed the brakes in...
The cylinder above started like this. That cylinder has been together for nearly 30 years in running condition, and was exercised several times annually.
Note the bevel at the top of the bore, next to the valves.
If you have a way to lay out the bolt hole pattern give it a go. A drill press would help getting the hole thru and square.
Indexing of the pattern is mute. If you can pilot one sprocket on top of the other accurately, use the original sprocket as a template and transfer the hole location.
You don't need CNC equipment to do this kind of work. It's simple work for a boring bar in an open set-up in a mill. The Rhovis could be mistaken but the bolt hole pattern probably establishes location of the sprocket while the bore is simply clearance.
75 on 12 tooth is indeed 6.25 to one...
Here's a few points for you to consider:
Besides sealing the combustion chamber, the rings also act as a heat path to cool the piston. Granted the skirt and oil splish also cool the piston but the ring is no small player
The second ring also seals the blow-by that gets past the top ring so...