What is the specification for distributor end play for a 1970 455? Should I shim it to factory specification of tighten it up a bit?

 

Since the distributor turns CCW its sucked down when it turns as opposed to going up for Chevies. It should not need shims.

 

ALMOST correct.
The reason the dist'r is forced downward onto its support pad in the block is because it is on the LH side of the cam. Brand C dist'r resides on the RH side of its cam, which is going upwards.

The direction of spinning of the dist'r is determined by the angle of the gears' drive teeth, and can be either way, as the designer specifies. Olds chose CCW for dist'r direction. Chevy chose CW. Presumably the engineers specified these directions such that the dist'r / OP drive gear is always pulling the cam aft into the engine. No good can come from pushing the cam fwd.

To answer the original question- "some" clearance is required. I would say around 0.020-0.100 should do. This is shaft end play OF THE INSTALLED DISTRIBUTOR, from down on its seat in the block to up against the dist'r housing bottom end.

There is no point in shimming it for more or less as long as it has "some", because the gear will always reside down on the support surface in the block. Assuming that it has enough movement in the dist'r housing to go down that far.

 

Thanks, this makes sense.