Once you are done getting the opening for the transmission centered to the crankshaft/transmission centerline, don't forget to make sure the face of the bellhousing is square to the block too. I had to use shims on my Lakewood scatter shield to get mine to sit square to the crank/transmission centerline.

Shims.JPG

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)