I changed the intake manifold because there was.

I changed the intake manifold because there was a little seepage to the outside on the front with the updated metal one. Everything went smooth. Simple job. When I tried to start the car it seemed like the engine was locked up. The crank turns by hand almost one revolution then stops. I have since removed both heads and the timing chains and the starter and it still will only turn one rev. The heads and pistons look perfect. Could something be in the oil pan? How would that be possible? I am out of options.