I got an XU10J4RS engine from a crashed 306 GTI6. The engine wasn't started up for about 9 months, and it seems to be stuck.

I turned the crank manually with a ratchet, while spraying oil to the cylinders through the plugs holes. I did it for long time. Then tried to start up the engine, but the crank didn't move smoothly.. it moved, then slowed down (almost stopped), and moved again, then slowed, and so own.. Also when turning the crank manually with a ratchet, I could feel this behavior where there were places that the engine was very hard to push.
What can be wrong with the engine? How can it be fixed?


For the worst case, if the block is stuck, then I thought of replacing the whole bottom of the engine (engine block with crank & bearings) from an XU10J4R engine. I take the engine head from my GTI6.
Can I assemble the J4RS engine head on a J4R engine block? What modifications should be done (if any at all)?
What are the differences between the J4RS and J4R engine blocks, cranks, bearings, build, tolerances, etc?