take this for what it's worth. i don't have a small bolt pattern wheel to measure, but i have a couple of SBP centers laying around i was going to mate to 15" hoops some day. they are slightly bigger than 12"OD. i just measured a 14x5 1/2" big bolt [4 1/2"] pattern wheel, and this is what i got. the center measures just a bit over 12"od like the SBP center. back space is 3 3/4". hoop inside diameter is between 13 3/8-13 7/16". these measurements were all taken with a tape measure. so ASSuming the BBP and SBP wheels used the same hoop, and the back spacing on a 5 1/2" wheel was the same between the two, theoretically they should fit, but ???
don't know if this helps or confuses you, but i tried.