[PxTx]

I was afraid you were going to say that. Since the motor is not going to be pushed hard, you could get away with some compromises in the effort to keep the stock bore size and/or stock (standard) pistons.

Speaking in generic terms, you'll want about .001" for each inch of bore. So about .004" would be about right. Now you'll want a little more clearance on a forged piston since they tend to expand more, but until they do there will be some piston slap. How much clearance will it take to straighten the bore?

Since the car will be used gentely, you may be able to get away with some looser clearances. Trouble for me is that you may start to approach a setup that would nto respond well to some high revs and that is kinda breaking the spirit of what a Z motor should be.