Here's how I got the pistons out of a Mercedes block that had had a head gasket leak and the ethylene glycol had literally glued the pistons in.
Before starting, the crank has to come out.
First I got a chunk of aluminum the same size as the bore, placed it on a piston top and gave it a couple of hearty whacks with a 2 1/2 lb hammer. The piston moved but was in no way going to come out. So,
I got a piece of 5/8" rebar and turned the block upside down. Placing the rebar inside the piston skirt, I knocked the tops out of the pistons. IMHO someone who gets into the cylinder walls doing this is either unlucky or careless.
Turn the block over and thread a length of small diameter wire rope around the wristpin, and out the top. Here's the tricky part, I used a hollow piston hydraulic jack and was able to run the wire rope through the center, clamp it on top.
Then I jacked the pistons out.

The first oversize is 0.5mm or 20 over. I bored the block myself at a high school auto shop and then had it finish honed with a Sunnen power hone. After the cylinders were honed to fit the pistons, there were still some small grayish-black pits visible. I put the engine back together and it runs great.

At that time, 1979, a new bare block was $1300. So I had no desire to bore any larger than I had to. Never had another problem with that engine. BTW, that engine had a forged crank and every journal showed the signs of being induction hardened. It was way too complicated but that engine was beautiful inside.

R.