RE: engine hydrolic locking
Honestly, it sounds to me like you have a really good ABC engine. ABC engines naturally have a very very VERY tight fit between the piston and liner at top-dead-center (TDC). The liner tapers down, and is actually a bit smaller at the top of the stroke than the piston is round. If the piston gets up there, it can be really hard to get this piston back down. THIS IS A GOOD THING, nothing is wrong with the engine. It's designed this way, really.
You should be able to free the engine up by grabbing the end of the prop in one hand, and something solid, the engine, or something like that iwth the other, and turn it. You'll never be able to turn it over any other way.
When the engine runs, the liner heats up and expands, creating the proper fit between the piston and liner, but when the engine is cold, you get this kind of effect. Once the engine has been run for a little bit, this will go (mostly) away as the parts wear a little.