Maybe Pat or Jerry can chime in and tell me if I'm full of crap or not, but personally I would be very hesitant about buying a block that has been pre-bored without the pistons.

If I’m not mistaken different type of pistons require slightly different clearance.....there is also the question of the final finish on the cylinders being compatible with the type of rings used.

Then there are the pistons themselves......although it’s not as bad as it was 45 years ago (god have I really been doing it that long LOL), I have had occasions where pistons have not all been exactly the same size within the set.

Maybe it’s just me and I’m being over critical, but I really hate going back into a freshly built engine.