Eddy dual Quad

I do not think you'll lose power if you select a set of carbs with a total cfm rating very close to what the 4bbl is now. Going to large on the set, IE; a pair of 750's, will just make it muddy some place and scream up top.
If your current 4bbl. runs great, and the cfm is an 800 or 850, then a pair 500's will be OK. A set of 390 Holleys would be to small. (780 cfm)
A pair of 390's to replace a 750 would be better.