From what you are saying it sounds like you need something that will allow you to precisely change the angle of the engine and hold it in place while you fabricate the parts. If so your challenge would be to find a practical way to adjust the height at all four points to allow for an uneven floor as well as the angle of the engine.
If I were faced with this challenge I would solve the adjustment issue by the use of bottle (or scissor) jacks at all four points. The base would have wheels that could be locked and the frame made of angle iron so it could be welded to the jacks.
Excuse me while I whip one up.
