I'll add my .02. About 20 years ago I picked up a hand held wide band for measuring A/Fs. The only caveat is you must install a bung in your exhaust downpipe. Purists can put this bung on the inside of the pipe so it cant be viewed from the engine compartment. On my 235, because of the 10% alcohol it leaned the mixture enough to warrant a main jet size. On my 261, I was able to run the standard jet but I have the correct larger Rochester B. Point is you can measure A/Fs that can be used as tool to for these sorts of things. Takes all the guess work out. I believe they are around $300 or so.
Steve

Last edited by sstock; 10/23/2022 12:07 PM.
1953 Chevrolet 3100
261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY Gallery
Video of the 261 running

1964 GMC 1000
305 Big Block V6, sm420, the next cab off restoration