Hey Jamie ,
If your looking at a Premier TITAN clutch it IS 3/4 inch bore , I have one !!!!!!!!!!
The minicup clutch is the same thing in the 1 inch bore .
I don't think that you can change the sprockets on the TITAN to run a 40/41 chain , I run a 35 chain and have no problem with it .
they are made for a four stroke , WORLD FORMULA Karts .
The clutch is rated to 20HP but the tech. guy told me that it would hold more like 25-30HP .