I think you would actually get less airflow by doing that. The 4779(750) has larger ventruis then the 650. the base plate of the 650 has alot smaller bore then the 750. So you would have a flat lip at the bottum of the main body where it meets the base plate. That will cuase a lot of turblence in at the bottem of the venturis. I think your asking for alot of probs by doing this. if you go to a few swap meets you can normally pick up a carb in need of a rebuild for less then $100. just make sure that no 1 has molested them. ( I have seen some pretty nasty things done to carbs by so called "tunners") I hope that makes sence... I am still way to hung over.