If you have concerns about too short of a piston, look at what a factory 454 chevy runs! The pistons look like hockey pucks to us Mopar guys.
A 512 motor can use a 6.535 rod, a 1.32 compression height piston for zero deck at 9.980. All shelf parts. They live very well, no need to worry about where the oil ring is. The rotating assembly is very light, and combined with the lower rpm it actually stresses the block less for the same power goals.