[dsraven]

consider this when placing the engine/trans.
drop a plumb bob to the floor and make some marks where the center of the rear frame is and then the center of the front frame. connect these marks with a straight line or laser or string-line etc. then when you get the engine in place drop the plumb bob again and mark the spot where the engine crank pulley center is and the trans output center is. this will keep the drive-line centered in the frame (parallel to the frame center line, which is not a square in some cases). when marking the drive line spots their centers should end up on a line drawn from the rear frame center to the front frame center. then you know the drive-line is parallel to the frame center-line. the same goes for the rear axle, it should be perpendicular to the frame so drop the plumb bob and do some geometry to figure that out. if the drive-line and the rear axle are not set up right then you will have a drive-line vibration. you shouldn't really go off the body because it is sitting on mounts and may not be straight with the frame center-line. the same theory can be used for the front end to keep it perpendicular to the frame center-line (and also centered).
just a few thoughts.