2bbl on single intake

At least you are using the adapter the correct way. I have a Carter BBD on my 273 V-8 with a 4 bbl intake, using a 2-4 barrel adapter upside-down (tricky bolts). I did as a temp before I change to TBI fuel injection and figured I could keep that setup in the trunk as a small backup.

I suspect easier to find an aftermarket 4 bbl intake for your slant today than a now-rare factory 2 bbl. Since "money is no object", look at the Hurricane intake (Aussie import, ~$600 but high-bling). Then, try to find a small 4 bbl (say 370 cfm) or perhaps better a TBI like some <$1000 now and allow swapping in smaller injectors. Sorry I can't give you the exact answer you want.