[geezer#99]

Marine carbs have plugged vac ports on the carb and are jetted richer because they spend most of there time at 3 to 4 thousand rpm. You can make them work if you're adept at pulling out the plugs and installing hose barbs. Likely not worth your time.
X2 on a small carb, langdon's headers and especially an hei. The hei will be your biggest improvement.
There are differences in the intakes too.
Clifford ones can mount your carb either direction. Some clifford's have heat passage built in for heat to your intake plenum.
Offenhauser intakes turn the carb sideways and you need a heat plate adaptor.
You might not see an improvement in mileage but you'll have a sweet looking and sounding motor.