I've been through this twice. My car came 383 4bbl. and I swapped in a 440+6. What I found (been a few years) is that the stock 4 bbl. cable did not have enough "throw" for a six pack. What I mean by this is that the length of exposed metal cable on the carburetor side was not long enough to fully open the center carburetor.

Also, the E-body & '71-up B-body six pack cables (available from Direct Connection since the late 80's) have a square plastic plug where it goes through the firewall & my '70 has a round plug hole.

There may be accurate reproductions today. I've also wondered how hard it would be to get a long'ish cable & trim back some of the outer black plastic to get enough "thow" for a six pack.

Both times I replaced mine I bought a used original part.