I’d also be worried about how the centerline of the converter as mounted to the crank lines up with the trans centerline, the pump bushing won’t like anything being off as I believe that is mentioned in the B&M paperwork. Think rapid bushing wear and leakage. Line boring of the block changes alignment, and while an oem flexplate actually flexes and is more forgiving the B&M doesn’t and isn’t. Pretty damn rigid as I’m sure you’ve noticed. Have you checked crank pilot depth, and the converters pilot? Difference in positioning from block/trans mounting surface of the oem plate vs. the B&M? Likely some hardened sae washers (Hillman brand at better hardware stores) is all you’ll need but lots to check over.
