Trying to rotate engine by hand
Any possibility the 2 cylinders with sp plugs may've filled with coolant & hydrolocked?
Or maybe any of the others were wet but now have rusted/stuck rings to cylinder wall?
Get all 8 plugs out & Like wrencher said ... penetrant in all 8 holes. Then like moneypit said ... big flat screwdriver or prybar on ringgear.
I use WD to displace water. It is not as good as the other 2 that are for Loosening rusted or seized parts.
Take your time and you may be able to save the rotating assembly.
Good luck, and keep in touch!!!
1/2" drive breaker bar and a piece of pipe on that as a cheater bar.....Did you try going back the other way with the rotation????Sometimes something will break inside the engine and bind in 1 direction only.Going back the other way,you may be able to get to it from the other side of the rotation.
Good luck with it,hope you don't have to pull it with the converter






