Could be most anything since someone else did the swap. First step would be to measure if the engine location is correct. If the engine is in the wrong location then fix that. If the engine is in the correct location then go to the next step. Are you going to leave those manifolds on there or put on headers? If the engine is in the correct location then perhaps you need to find a set of the correct manifolds. Have you verified that the transmission mount is correct and properly installed? How does the driveshaft look? Is it correct with the right amount of end play?