I just freed up a 1956 Fleetwin after soaking it for several days in the 50/50 (acetone – ATF) mixture followed by setting fire to it. The pistons were in the bores even with one another (advantage). I took a couple of old cotton socks and cut them in strips and soaked them in ATF, stuffed the socks in the boars and lit it off. Sucker burned for darn there 30 minutes. Let it cool and tap tap with a wood block and shazam, she freed up.