When you say your going to rebuild the engine with 10.5:1 pistons are you going to blue print it to make sure the compression is 10.5:1 or are you just planning on using a set of 68-71 340 hi compression pistons ?

The factory style pistons wont actually yield a 10.5:1 compression. With a stock combustion chamber/valves and a .040" gasket youll be closer to 9.5:1 and it will run fine on pump gas.

My 360 is 10:1 compression, closed chambered 302 heads and a comp cam XE268, It run fine on pump gas.