Chrysler-dodge used 2-4 barrels on B and RB engines in the late 50s and early 60s. It's one or the other.
I have nothing to base this off of but a hunch, factory Cadillac dual quad? I know they had them and from one of my customers 8 year search for his they are pretty hard to get.
By the casting number that manifold was used on 58 Mopar 350 (yes, 350) V8 and 59-61 383's. It's easier to identify engine castings with the casting numbers if you have them. Luckily on this picture it was fairly easy to see.