Freeing up a frozen block ??

First, did you go ahead and pull the ones that you can reach?

I'm assuming motor is on a stand?

I've had the best luck with any kind of penetrating oil, and then using a prybar on the counterweights with mar-protection on all contact points. (FYI Excalibur, my preferred prybar, is 48").

Conversely, if it will hold water, you can wash all the oil out with brake cleaner and fill the cylinder with water (unless it's at TDC) and use the electrolysis rust remover trick. It will pull rust out of all sorts of nooks and crannies, which is what you really want because the rust is mechanically locking it in place.

ETA And I would ignore the naysayers. This is exactly the kind of project that you can learn on and if you break something....meh. Then you'll know better when you score that locked up 340 at Pick n' pull and don't want to mess it up.