Slant 6 offi 4 barrel intake
Looks like your car now has a 2bbl manifold with a Progressive carb. I like those Progressive carbs, use them on our VW 1835 cc Dune Buggies. Good response with a secondary.
The 4bbl Offenhauser manifold and adapter could be adapted back to fit your Progressive carb with this 2 to 4bbl adapter. Or 4 to 2 bbl . . .
Available at Advance Auto Parts for 20.00 bucks, the old Carquest stores.