Phenolic resin from what I can remember? Those carburetors have great potential, but poor parts support, and whoever designed the choke, fast idle, and other linkages was on LSD back in those days. I absolutely HATE working on those carburetors for that reason.
They are also too wide for a clean fit in many applications, rear fuel inlet, and too high in the casting to clear most factory Shaker, Ram Air, or aftermarket drop base air cleaner set-ups.
This makes the q-jet a better option, as it has PLENTY of parts support, and much more compact, with a front located fuel inlet low in the casting......Cliff