For a SBC that would be considered too big, but not so for the 351C. The 351C likes 2" header primaries too. Unheard of with a SBC. The mighty Clevo breathes big. What other 350 cube american V8 could make 500 streetable BHP in 1973? What other 350 cube American V8 was competing successfully against the big blocks in NASCAR racing in the early 1970s? yeah, I kinda get passionate about the 351C.
I've seen some people having tuning problems drop down to a 700 Holley and have better luck. In days long ago a good choice was the readily available 735 Holley designed for the 428 Cobra Jet. It came out of the box fairly well tuned for the street. Back in those days the 4779 double pumper & the 3310 vacuum secondary were jetted really rich in the low speed circuits. Holley designed those carbs for engines with hot cams and not much intake manifold vacuum, so to compensate for the lack of intake manifold vacuum the lower speed circuits were richer. This resulted in poor drivability and sluggish low speed response to the throttle. Todays choices are much better between the Holley HP series, the Barry Grant carbs & the various "tuner" carbs out there.
Just remember if you're buying a BG carb, you want about a 650, not a 750.
If a carb is rated for 750 CFM, it should flow 750 CFM. If it has fatter boosters in it, the manufacturer has compernsated for that somehow, to make it flow 750 CFM. You shouldn't have to stress over subtracting 50 CFM for the boosters & therefore needing an 800 instead of a 750, etc, etc. The tuners mill away the choke horns, smooth the entrance to the venturis, streamline the butterfly shafts, etc, to make a carb flow more CFM anyway.
When you buy a HP Holley, a BG Demon, or a tuner carb, you're paying a premium price because supposedly some "expert" has worked that carb over so you don't have to worry about it, just bolt it on and have fun. If it doesn't work that way, you've just spent several hundred extra dollars with no results to show for it.