I agree, I recently tried to tell someone I was worried about my pinion angle and engine angle on my 67 project because I am mating a BBC to a T-56 tranny and a 9-inch Ford. They tried to tell me that none of it mattered...it would not vibrate...because the driveshaft would take up the "slack" and angle diffs. I said that the angle of the engine..down..should equal the angle of the rear end..up..but oOOHH no he said, dont worry, just put it all in and it will work....sure..whatever, As these PROS! said, match those angles, cut and weld a crossmember to work and you will be ahead of the game! There shouldn't be a problem moving the transmission mount ahead or back as long as you can work out those angles, so just...for lack of a better word 'Shim' the tranny mount till you get your desired angle up front and so on and so forth, be wary that some rearends like to 'twist' once disengaged from the driveshaft or torque bar..if equipped, so the effective angle at an uncoupled moment may be different than at an operation moment, this touches on what tech said about the operation condition of the diff as you drive, under load the pinion will try to climb the ring gear (also incurring evil, axle thrashing wheel hop) and also give a slight degree change...uh thats enough for me, have fun...swaps are what this hobby is all about.