Given that I have a 400 originally from a 67' GTO transplanted into my 67' Pontiac Firebird (which presumably originally had a 326) I likely have a mismatch between 2-line and 3-line configurations. I currently have a 3-line after market pump on the engine where the vent line was blocked off and I cannot find a vent line - so either there was a vent line originally on the 67" Firebird and it was removed or there never was a vent line.

I have the options of installing a two-line pump (Carter M4523/vertical female input or M4689 /lateral female input) or installing a 3-line and new vent line. I live in CA and the car will be in hotter temperatures so having vent line may be beneficial. Note that I did have the gas cap issue previously and did get the correct vented cap through Ames which solved the issue.

So, three remaining questions are:

1. is the M4523 or M4689 the right product (as the female inputs are at different angles),
https://www.summitracing.com/parts/crt-m4523
https://www.summitracing.com/parts/crt-m4689

2. these products reference 2 BBL but I have a 4BBL - any difference? and
3. should I install a third vent line for warmer climates.

Thanks again.