While they may be the 72-73 8.5:1 compression pistons, that doesn’t necessarily mean that’s what your compression will be. Those look like the pistons I have but my compression comes in at 9.0:1.
Ok, but you have to know how far the piston is down the hole (or how far out of the hole they are), chamber volume and head gasket thickness and bore diameter to know what he has compared to what you have.
At best, as yours appears to be a best case scenario the OP is still a long way away from 10.5:1 no matter what.