big bolt pattern for 7-1/4 rear??

There are LBP and SBP 7 1/4 rears, but they each have there own axels, and housings. You cannot swap a LBP axle into a SBP housing.

I'm going to check you on that statement. :D

Reason I'm even questioning it, is that I believe I vaguely recall pulling axles and finding that the bearing set-up is different between large and small pattern.
I wasn't pulling the axles to use, I was pulling them to remove 7-1/4 housings for cores for a specific non-mopar related application and noticed the difference, but I'm not 100% sure.

It won't surprise me, if true.

Mark.