So the only problem right now is the engine can not revolve 1 complete revolution
Can you turn it a full revolution by hand with the spark plugs removed ? ( two is even better )
If you turn it backwards does it stop at the same spot ?
Does it stop with click, klack , thud or just bind up ?
Is there any damage to the spark plugs ?
Had the gap closed up?
What sort of colours are the insulator noses ?
are they both the same ?
Do all 4 pushrods go in & out the same distance ?
If the engine is a single then the counter weight runs on the crank and goes back & forth between the crankshaft & the end of the crankcase
If it is a twin then there is no counterweight .
We can not see, hear smell nor feel your engine so you have to describe what is happen as if we were Tommy , the deaf dumb & blind pinball wizz .