Are the heads off? There's a bunch of different ways and you may need all of them! Oxy/Acetylene torches with a "rosebud" tip, lots of penetrating oil, or make you're own with acetone and auto tranny fluid 50/50 mix.. Also a big block of wood that fits the bore real well and a Big F'n hammer, give'em a few wacks and even use combinations of the above to shake'em free.

On another site I frequent, they play with large stationary motors and those guys even go so far as using charcoal briquets and getting things real hot and then let'em cool enough to smack'em with the hammer deal.

I did a 427 Ford last year and it took me weeks to get'em all out. The hardest part I thought was that I couldn't turn the crank to free the nuts of the pistons that were free! Also I used the flywheel ring gear to help add pressure. Hope this helped.