Welcome, Chris. I'm no expert either, but it appears that there are two lengths of the intermediate shaft, 5.75" and 6.125". From the little bit I've searched there are different combinations of block & pump that dictate which you need. Apparently lots of guys with SBC's elect to run a BBC pump? From your description it's sounding like you need the longer intermediate shaft, but to add to the confusion some of the aftermarket guys, like Morosso say in their specs that their shaft differs from stock by 1/8".... Again, different combinations of block & pump. Wish I could be more help.