What is the differance between all the sb distributors? Is it just the way they were curved?

Fundamently, yes. There were cast iron dist housings and alum housings. The early distributors were iron and the later ones (about the early 60s) were alum, EXCEPT the Corvette and some truck distributors which were iron. Up through 1974, the Corvettes had point type distributors, they were cast iron and they had a tach drive on the side. Some did, and some did not have vacuum advance.
For the most part, your basic, vacuum advance distributor for PASSENGER cars and LIGHT trucks (BOTH BB and SB) were all alum. The MAIN differences were vac adv can, adv weights and springs and the cam on the top of the shaft where the weights made contact.
PHYSICALLY, all SB and BB distributors will interchange. That is, you can acutally remove a dist from a 454 and stick it into a 57 283, regardless of whether it is point type or HEI. The old 348-409 distributors ARE NOT interchangeable with SBs or BBs. You can also do the same with a 55 or 56 265, BUUUUUUUUUUUUUUUUUT, orientation of the distributor in those engines is critical because they are dependant on the positioning of the groove at the lower end of the dist housing (for oiling purposes).
Hope this helps.

Yes, it helps! Thanks