i would try to flush the bearing with gas, or carb cleaner, and see if something comes ou, like dirt, or is it one spot on the bearing? use a paper towel to collect the run off. if the race is flaking, or has play, don't run it. it has to turn smoothly. you may be able to find a used drop in crank for cheaper than rebuilding yours.
the head can be milled, but i wouldn't use a belt planer to do so; they tend to take off material more on one side, than the other, leaving it flat, but uneven. it is possible, with practice, and constant re-orientation over several passes. the stock heads vary in chamber size, so you will have to measure the chabers before, and after, shooting for 21cc, if you are under 1000ft asl. you can do this, by using a piece of plexi, cut a small hole, and fill with water, and empty it with a syringe to measure. start wit a .020 cut to get you close. around 150-160 psi, switch to 50/50. on this, i am assuming you are around sea level, have pipes, stock timing, and not to wild on the porting, or that may change things a little.
as for the clutch gear, it shouldn't have play by hand, but there are bushing kits out there to rebuild them, if the basket's not groved.
this is my.02, and would emplore you to take advise from more ppl than me, because there are several on here with way more experience than me, banshee specific :thumbsup: