STEVEN N. - I rebuilt a 14 HP Kohler starting over 4 yrs ago. I used all OEM parts plus a couple heavier-duty parts similar to the Killer Kohler suggestions listed on the write-ups on the pulling forum. So far with about 100 operating hours I'm constantly amazed at it's performance. There really isn't a "rebuild kit" of parts but these Kohlers are pretty simple and basic. First thing is to disassemble Your engine and inspect the old parts. Check the piston top to see if there's markings like "010", "020", etc. That's the marking for over-size pistons. It determines which size the new piston & rings need to be, You need the next size larger O/S. I got by using a +.010" O/S piston/rings/wristpin and had to grind the crankshaft throw down .010" undersize. Grinding the crankshaft requires a new connecting rod, but they're a wear part on Kohlers anyhow. I've never reused conn. rods on ANY Kohler I've ever rebuilt.
Grind the valve seats, replace the exhaust valve, install ALL new seals & gaskets (avail. as a complete kit) rebuild the carb, install new ignition points & condensor & spark plug & plug wire, new air filter and Your K321 will run like new for MANY many years.
I spent several times more to rebuild My K321 than what I paid for the CC #72 back in 1981 that I installed it in. With OEM parts and machine work by a competent shop You should be able to rebuild Your K321 for $400-$500. You can save some $$$$$ by using parts from STENS, They're good parts also and can save You possibly $100 total.