Did you also verify that the bellhousing's transmission mounting face is square to the back of the block? Mine are usually off a bit from square, and I use hardend prescision washers to adjust that.

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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)