I am building a budget 393 stroker from an 83 351w block. I plan on using 302 pistons, 351 connecting rods with new crank and cam. This is just for fun project so if I tear it up, no problem. My question is with the 302 pistons I have a piston to cylinder wall clearance of 0.010". Will I have piston slap? Will the rings ever seat.
Make sure you are measuring the piston in the correct location. Usually its about 1/2" up on the skirt. Every mfg has their own specs though. I took a 393w apart that had around .012" piston to wall clearance. Surprisingly it didn't make any noise and ran strong. I got it from another member on here who was running 10.80's n/a with it. You'd be putting a time bomb together, who knows when it might let go. 302 pistons are easy enough to come by I'd just go oversize if possible.
Check your bore too. Make sure that you don't have any taper and that your bore is round. If you are at a stock bore now I would only go to the next size if it will clean up. If it will clean up at .010" over use that, it will give you more life out of the block by being able to go larger in the future.