I would be curious if something is in with the timing chaining bound up
My thought as well. Something small dropped down the cavernous opening at the front of the head and is jammed between the timing chain and sprocket. In which case the OP would still be at the level of disassembly he is in right now.
It could be several things causing the engine to be ( or appear to be) seized, but more perplexing to me is the coolant on top of the head.