ive dealt with alot of frozen engines and the best luck ive ever had was with pb blaster. make a pool on top of each piston and let it sit for a couple hours, roll it over and try to pound them
out using a wooden dowel or hammer handle. if some still dont move, dont rule out frozen wrist pins, i had a locked up 383 because of 1 frozen pin. if this is the case fill the bottom of the piston while its upside-down and try again later but be careful for cyl. damage as the rods may not move smoothly. good luck