The clutch will work but it's not the heavy duty clutch that the 800 has. The brackets are also different. You can find the brackets on E-Bay.
I just got done putting electric start on my 05 700 RMK from a 05 600 Switchback and it was a lot of messing around to get the right parts to fit but it is doable,
A few years ago I put electric start into a 600 classic that I put a 800 motor into. It was a challenge but it worked out good to a point.
In the cold weather the old 800 doesn't like the cold and I bent the armature in the starter motor trying to start it.
Anything is doable if you do the research.
You will also have to make sure the rectifier is wired properly so the battery is getting a charge.
Take your time and read the wiring diagrams and it will work.