How much difference between a '81 kz 650 and kz750?

Are these somewhat interchangable? I have a motor for a kz650 that isn't being used and a chance to get a kz750 donor with out a motor and was wondering what parts I maybe could use.

Thanks

del

If your 81 KZ650 motor did not come with a kickstart, then it is pretty much the same as the 81 KZ750 motor. Same crank, rods, cam chain, intake valves, etc, however the cases are a little different (so are the exhaust valves).
It should not take more than a couple of spacers (you can use washers) to bolt it in.

The KZ750 head, cams, block, and pistons will bolt right on using the 750 (or 650) cam sprockets because the non kickstart 650 motor uses the same HyVo cam chain.

The 650 is a non-kick start model. The way it sounds is that almost everything is able to swap then if the frame is the same. Right.