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The only difference you'll really find is that you'll be able to more easily run the newer engine without smog equipment with the older carb. The 80's carb will run slightly lean without it all hooked up due to it being calibrated for emissions.
Other than that, they should be very much the same as far as flow rates.
Well I think I will just keep the '67 carb on the '67 motor. we don't have smog regulations here so I don't have to worry about that. That's why I'm putting an older motor in my truck. No smog.
Generally, when you change engines, you must pass emissions requirements for the newer of the vehicle or the engine.
If you put a new engine in a old car, who's going to know, since it's exempt from testing.
If you put an old engine in a newer, emissions test required vehicle, and think you'll just be able to wave them off by telling them it's a '67 engine, you have a surprise coming.
Your engine change will come under "Emissions Device Tampering" unless you bring it up to 1980 spec (if that is the year of your vehicle)