Motorhome carb size?

Quadrajet carbs came in many different CFM sizes so I wouldn't say for sure it is a 750 Carb, unless you have some evidence.
My experience with a Holley 650 Spreadbore replacement carb has been very positive. They are an exact fit replacement so the fuel inlet, throttle attachment etc are direct hook up, BUT the spreadbore Holley is a double pumper carb. They run FANTASTIC with the factory cast iron intake manifold.

Good Luck!!

George