If the pistons are stuck in the bores, soak the cylinders in something like PB Blaster or KROIL for a few days, then use air pressure to blow the pistons out of the bores. Wrap the wheel cylinder in rags or hold them in a smooth jaw vise with the pistons facing the jaws so they don't launch themselves across the shop when they break loose. Once one piston is out, the other one can be driven out with a wood dowel rod and a hammer. I have honed hard to find cylinders way oversize and made new pistons on occasion. Wheel cylinder cups can expand several thousandths to accommodate an oversize cylinder bore as long as the pistons fit without wobble.
Jerry
