In my '70 DH43N0D, with the "N" meaning 383 4 bbl HP V-8, rated at 330 horsepower (there was no 325 horsepower version in '70), it had a Carter AVS 4732S on it from the factory. Factory a/c and TF. When I was trying various carb insulators on it, I managed to crack the baseplate near the vacuum advance take-off port, so I ended up with a 4736S on it, as a Carter replacement. Seems like the 4736S replaced both the Federal spec and California spec carbs? Be that as it may.
The factory cast iron 4bbl intake for the '70 383 4bbl is about normal in all respects, but one of the Edelbrock Performers might work better in its place. I need to specify "normal" Performer, not the Performer Air Gap or Performer RPM variations.
In many respects, as you are not in the USA, you might be better off getting a new 650 cfm AVS from Edelbrock, via Summit Racing (as they typically have the best price on them). The main thing about using an earlier OEM carb is that the fuel curve might be more dialed-in than the aftermarket AVS might be. But if you check the metering rod/main jet sizes in the OEM carb (listed in the factory service manual carb section), that might get you a little closer. Remember that when the car was new, the gas had "lead" in it (and plenty of it!), whose amount has been reduced/eliminated in later years. Ethanol content was much lower back then, too, with lead being the main octane enhancer back then. PLUS, all of the internal fuel and air passages (metering calibration areas) will be CLEAN whereas even if an older carb is soaked for days, any harder deposits will NOT be dissolved by the solvents, needing to be mechanically removed with small twist drill bits (which very FEW people know to do!!). Plus the throttle shaft bushings will be new and tight. By the time you find a good carb to rebuild, then pay to have it done, you could be pretty close to the price of a new carb (with all of its benefits).
The throttle actuation is via cable, which would be unique to the type of carb, typically. So one of the correct length would be needed for the AVS application. I know of no repro cables for C-body cars, but there should be some for B-body cars (Road Runner, Super Bee, or similar) with a 383 4bbl motor. A different trans kickdown rod might be needed too (see comment later on), between the adjustment point at the rear of the intake manifold and the carb stud. The carb cable stud, where the throttle cable attaches to the carb, can be re-used with a new carb, so don't discard that.
The fuel line will be different, between the fuel filter and the carb. You can probably get one for a Road Runner 383 AVS car from a repro vendor, possibly.
The 2bbl air cleaner will have a smaller diameter mounting "ring" than the AVS can use. A quick fix is the repro '68 Road Runner air cleaner assy from Mopar Performance. The factory air cleaner on my car is a crinkle-finish dual snorkel unit, with the vacuum actuator in the lh snorkel. Used, they used to be close to $300,00 USD at the swap meets.
With which ever carb you end up with, use the FACTORY-spec thick carb insulator gasket. The extra thickness is necessary for best performance! They ARE available from Holley, having a divider down the middle, front to back, rather than being open or having 4 specific holes. The divorced automatic choke would need to be replaced with a AVS-compatible unit, BUT the Edelbrock AVS can be had with an integral electric choke instead. Another reason to get the new Edelbrock AVS.
My '70 Monaco 383 4bbl came with the "small" 10.75"torque converter. It takes one quart less fluid than the 2bbl converters, which are of larger 11.75" diameter. As a result, the stall speed was a little higher for a little "edge" in off-idle acceleration. Not a significant deal with a 2bbl to 4bbl upgrade, to me.
Your 2bbl, unless it was ordered otherwise, should have a 2.76 rear axle ratio and had either G78x15 or H78x15 tires. Modern equivalents would be P225/75R-15. That tire/gear combination would yield about 28.6mph/1000rpm on the highway. With the optional 3.23 ratio, right at 25mph/1000rpm on the highway. The 2.76 was option with the 4bbl cars. Makes a 90mph cruise with the engine on the top of the torque curve at close to 3000rpm.
The trans kickdown rod adjustment is slotted, so you might be able to extend it to work with the 4bbl carb. Have to see about that as a final thing to worry about.
One last thing might be an upgrade to the exhaust system. The 383 4bbls had "hi-rise" exhaust manifolds where the 2bbls typically had "flat" log-style manifolds. These can be had used, from time to time on eBay or similar (even in the For Sale forum HERE). From there, you'll need to build a dual exhaust system or purchase one from Waldrons or similar. But this can come later after the 4bbl swap is completed. It takes the dual exhaust to enjoy the benefits of the 4bbl set-up. The better cast iron exhaust manifolds complement this.
Now that I've mentioned these things, I'm curious what you're seeking with the change to a 4bbl? As it stands now, your existing carb is basically the primary side of the 4bbl, air flow capacity-wise. Any additional power will come only above about 2800rpm at WOT. So, general "drive-around" feel will be pretty much what you now have. Just curious.
Just some thoughts,
CBODY67
