Alex Tucker,
From the 1967 Mopar shop manual re carb jets for a 383 engine.
Carter 4298S manual trans:
Primary main jet: 0.089" (carter # 120-389)
Secondary main jet: 0.068" (carter # 120-368)
Std primary metering rod: 0.064"-0.063"'-0.055" (Carter #16-404)
1 step lean metering rod: 0.066"-0.064"-0.058" (Carter # 16-171).
Carter carb # 4299S auto trans car
Primary main jet: same as std trans car
Secondary main jet: same as std trans car
Standard main metering rod: 0.062"-0.059"-0.051" (carter # 16-475).
All metering rods are three (3) step and can interchange. 3 step rods use a domed cover plate and are different from 2 step rods, which used a flat cover plate . The step up piston and spring are different lengths than 2 step piston and springs but are the same diameter. You can substitute 2 step pistons and rods for 3 step pistons and rods but you need to use the correct cover plate.
REMEMBER because the metering rod is fitting inside the jet, if you want or need to know the equilivant jet diameter, you must do an equivalent AREA calculation, subtract the areas and convert that number to a equilivant diameter. You CANNOT just subtract diameters because area varies as the square of the diameter (A=3.14 x r squred).
Search the internet for Carter carb parts....not just the Edlebrock Carter jet kits as they are only 2 step tods. Also scour the junk yards for old cars.... early GM was a great source for both 2 and 3 step metering rods pistons and springs....B4 they switched to predominantly Rochester carbs. I used to raid the junk yards....most of the time the junk yard owner's did not care what you removed.....and simply just gave me these small parts.....
Bob Renton