engine angle

[CMcAllister]

If this is a typical big tire backhalf car with the rear u-joint CL higher in the car than the front joint CL, having the engine nose down will help achieve desired operating angles on the joints while keeping the pinion angle negative or nose down - which is desired in a drag car.

Otherwise, using the OE engine 3 degree down in the rear mounting, you get into the "broken back" arraignment.

Plus, the oil pan, headers, steering, etc all have to fit each other. It takes some planing and time mocking things up.