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They're mechanically interchangeable between SB and BB, but the part numbers are different due to the different centrifugal advance weights and springs and the shape of the autocam on top of the mainshaft (all of which determine the specifics of the advance curve for a given engine application), and the specs of the vacuum advance unit for each application. They're the same except for the tuning items.
I think you may have misunderstood John's post. Distributors didn't have a casting number, the part number was stamped into the same tag as the date stamp. 68 390 & 400 BB's with TI were part number 1111294, 68 L-88 used 1111295 and 68 435 used 1111296. Appearence wise, a 69 SB TI distributor becomes a 69 BB distributor with the addition of the correct tag. The tags are reproed by Paragon.
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.