Well after replacing the lifters in the chevelle, I noticed the shim on the distributor was broken and all tweaked out of shape...indicating that I don't have enough clearence for the cam or oil pump shaft...so heres the plan.

Shim the distributor end play back to .010"-.015".

Question however, what is the best way to measure how much shimming you need between the intake and the distributor to make sure you are not bottoming out the gear and losing all your endplay you just put in? Also how much clearence should you have and does that with or without the distributor gasket.

Shim the dist to where it needs to be, out of the motor.

Then install it, with the gasket; and see that it has the same end play when in the motor, that it did out of it.

Mike,
You did not mention what kind of distributor, but I read somewhere that HEI's need a lot more end play due to the expansion of the housing. Don't know how true it is but HEI's always seem to have a bunch more clearance.