Jay, what engine spec Kohler are you using?
There are 2 different styles of closure plates on the kohlers, ones where the bolt face is smooth, and ones where there is a pilot circle cut into them. You would like a smooth one, but I think you can make either work as long as your holes in the clutch line up. I believe I had to file or drill the clutch holes out just a touch to work with the bolts needed for the Kohlers.
My experience(2 complete repowers) is that you need a spacer between the shoulder(actually a chamfer on the Kohler 1 7/16" crankshaft) and the clutch itself, and then a long one after the clutch to take up the extra length of the crankshaft that sticks out of the clutch. That one all depends on what length of crank you have. And you want it a bit longer than the extension so you get clamp load.
If you make the one behind the clutch too narrow, the magnetic coil rubs on the clutch and it fries itself. My 420 repower I made the spacer myself, but with the chamfer not shoulder on the crank, when I tightened the big bolt on the end of the crank with an impact I smooshed the spacer more and after a few hours of running the clutch failed. Next time I hand tightened it.
These guys sell the spacer you need for behind the clutch:
Some times when you call they will only want to sell you the whole kit, other times they will sell you just the spacers. Maybe Barry is the guy to talk to, been several years now.
Piece of cake right?