BB motor mounts for 71 two-wheel drive

[BBC Motorhead]

I am at the beginning of a frame off on my shorty and I am starting on the frame and suspension. The truck was a sb truck originally so I don't have the oe bb mounts. I found some really nice custom made tubular ones online from a company called performance online. The nice thing about these is they are the newer style mount than the original. They told me they will work with SB or BB-the same set. I am wondering what was actually different between the two from factory. Any and all info is appreciated. Thanks in advance!