Compressed air at 150psi is no where near the pressure in a hydraulic brake system, you'll never cause a caliper piston to split with air pressure. I've used a portapower pump to remove caliper pistons before and they will reach 10,000psi.
Unless I'm mistaken, the caliper on that bike doesn't split. It's not like modern Brembos, two machined halves joined by allen bolts; it's a crappy floating caliper design with just the one piston. In which case, a grease gun is your only real friend. Once it's out you can use a lathe to knock up a replacement stainless piston, but that's about it.
I'd just buy a new piston as they are fairly cheap from various suppliers, try swallowing the cost of replacing 8 pistons and seals in a more modern bike twin disc setup!
