you can position the clutch anywhere on the shaft.
If you are struggling with how to HOLD it in place, just use spacers. Some clutches have a little set screw but some have complained that that isn't enough.
A bolt goes into the shaft on the end with a washer that holds the clutch/spacer(s) in place.
You can get some 3/4 or 5/8" pipe and cut it to size for the spacers (depending on engine shaft size).