Carter 383 2bbl for SL6

Those larger carbs won't bolt on, but they should!
They average right around 375 cfm, are dirt cheap and easy to find. In my opinion, with the right jetting they are the PERFECT choice for a mildly modified Slant.
For the time, effort and cash people sink into their 390 Holley's, you could fab an adapter, set up the carb, and probably have enough left over for a set of headers.