With a better piston like SRP,JE,Ross etc you really don't have to do the 'fit to the hole' so to speak. I mean it's not anything like the ol TRW sloppy tolerances. With the better pistons a big part of what your paying for is the finish tooling and repeatable size from piston to piston to piston. Not as tho having the piston in hand to verify size isn't a good check, but it's not as big of deal as it used to be.
If the block is final honed with a stress plate, and decked to your spec, then I'd say that is a very decent deal. But... I'm guessing it's not stress plate honed, and deck is 'as is' unless they see damage and 'touch it up'.
With a new virgin GMPP 4bolt block being $700 now, what you found there sounds like a decent deal. But quality of the final machining will the the test.
One of the best guys I know of for shipping high quality cnc machined sbc block is Carl at
CNCblocksnortheast. Seen a couple of his pieces and they are first rate. Might be worth a call to see what he can do for you.