Without knowing what list #'s you have its impossible to guess.

Here are the differences in the 4779 (750)     and      4780 (800)
    venturi diam. primary           1 3/8                        1 3/8
    venturi diam. secondary       1 3/8                        1 7/16
    throttle bore diam. pri/sec    1 11/16                     1 11/16 

My old Holley catalog shows different throttle body & shaft assemblies for these two carbs.

Get the List #'s and I'll check by book.       

thank you for that crewchief. the base plate that im looking at isnt a holley and says it fits all holley 4150 carbs. to the best of my knowledge holley no longer makes the base plate for my carb.