According to our records for factory Nash/AMC, they only offered 2bbl & 4bbl options on the 327ci Nash v8. Special oem version Holley carburetors for both as well.
Many years ago I bought several of the AMC / OEM Holley carburetors from New England Speed Equipment Co. I had a friend that worked there, and he took good care of me. IIRC they cost me about $ 50.00 each
Since it's a dry intake manifold, and the engine has a separate valley cover, it would be one of the simplest to fabricate. Also, are you familiar with Bill Kraft Rambler that built a drag car in 1964?
Old post but…I know a guy that converted a later after market intake to fit. I believe 2” spacers were fabricated to match up the ports but he used an edelbrock air gap.