The bottom end isnt really that hard... especially if you have a manual... Is it the stock manual? I have one for my RMX (89) and it guides you through in detail. I would recommend taking the crank to a shop. My manual doesnt say the max play either.
Are you talking about the rotor? Or the halves of the crank? If your talking about the rotor you may find this interesting... Prolly wont want to try it, but i think its interesting..
Ive got something goin on with my flywheel and stator. The 4 magnets inside the flywheel broke and beat my stator to the point of no return... So, instead of buying nearly $400 of oem stuff, I found a RM stator and rotor off of an 88 RM250 for $50. So i got the rm stator and rotor thinking rm, rmx, basically same thing, should work. WRONG. The crank is bigger on the rmx, so I had my shop teacher at school bore it to the size of the rmx. Made a new keyhole too. RM key is wider by the way... So I got a RM key and made a step-key to fit the RMX hole in the crank. Rotor is fairly thin and I hope it doesnt crack, but it works. Now the stator isnt as tall as the other either. So we spaced out the plate, and the magnetic pickup. Now Im waiting on gaskets to put it all together. It does have spark, so i think it will work. I should have it together sometime next week. I'll let you know.
Sorry for the loooooong reply, and that i couldnt help more,
but it may help a little.