Actually, if the motor mounts have been installed correctly, there is an offset to one side in the engine bay. They started doing this around the early 60s to give the side to side balance and the driver a couple extra inches of clearance for the pedals. Now, highly recommend removing the engine and attaching the transmission to it, then (I figure you have the hood off), remove the transmission crossmember (couple bolts on either side of it to the unibody), jack the front of the car up about 18-24 inches, slide the whole thing in, raise the transmission tail up and install the transmission crossmember, goes in a whole lot easier that way. From there you will be able to tell any offsets, which in the past, Schumacher has been really good with their adapter motor mounts. Doing it this way also helps prevent that 100+ transmission from being a bear when installing on the floor (it isn't that fun).