I have run it a couple of year with both an 4781 DP and a Pro form 850 DP and I also have an 3310 on the self... but no on that one.
It run cleaner and has more crisp throttle response with the P/F 850 but the 4781 was overall faster on the track, but it running pig rich on part throttle when is tuned for 12.5 A/F at wot.

P/F 850 is 1.75 X 1.40" If I remember correct and the 4781 is 1.75 x 1.56" venturi. I thinking it may want more cfm because it was faster with the "bigger" 4781? Well, do I need a bigger carb?