AC superseded pump models over time. The government forced manufacturers to stop using glass bowl fuel pumps (breaking during an auto accident). Around 1951, the pump arm length was changed to increase pressure by 1/2 psi. The Master Parts book lists angled output for 1937-54. The 1971 Chevrolet Truck Parts lists 1936-1957 as 5593247 and 1958-1962 as 6415726 which are the AC supersede replacements which have the crimp tops. As much as I like Carter, the M2999 is not a pump that Chevrolet used when building a new truck. A 1962 235 engine in a 1950 Chevrolet truck means the truck is not original so the owner is at liberty to use whatever he/she wants.
Ethanol gasoline can ruin a perfectly good working NOS fuel pump. So, if you live in an area where non-ethanol gas is hard to get, you want a pump that can withstand ethanol.
Let's say you find a used pump that will work on your engine, and visually looks like what you want, chances are it is worn out inside. The pump cam rides on a pin or pivot that is pressed/attached into the pump housing. After billions of operations, the cam, pin and housing have wear. So, to make this pump work well it needs to go to a professional rebuilder who can replace or fix worn parts and install ethanol tolerant diaphragm, seals and valve. The last time I looked, rebuilders do not repair Carter pumps. This may have changed by now.
You can buy new pumps from your FLAPS but these come from Asia. Finding a good one is hit-and-miss (i.e. reliability is suspect). If it fails under warranty, you get another one without warranty. If the replacement fails....
I bought a new pump from my FLAPS but I opened the box to make sure it was the "appearance" I wanted. I also bought a NOS AC pump just in case.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
