Total newbie rear end question

[harley]

I was researching ring and pinion gears for my newly aquired 63 SWB and realize I am just about clueless

Current gearing is 4.11 and I want to go to about a 3.38 give or take, open to suggestions also.

Anyway I finally called Randy's Ring and Pinion for a quote and that's when I realized I am clueless. He asked if it was a 12 bolt rear and whether the gears drop from the front or rear. Uhhhhhhh, I dunno

There are 12 bolts on the rear end but how do I tell if drops from the front or rear?

Pardon my cluelessness