Sealing the carb to the bottom of the hood does work. My brother ran his car without the sealing pan and it would blubber a little at the top end. Not bad, but you could tell something was amiss. Only when he installed the pan and foam to the bottom of the hood did it pull clean all the way thru.

the front of each car is so different that only a wind tunnel is really going to tell you what works I'd think. Cars with recessed grilles (E-bodies) have a ton of turbulence that builds up in front of the grill at speed. Guy here has a purple 70 Challenger with a glass hood and the front edge bows up a lot on the top end. Enough that I would be worried about the hood cracking eventually. How does a hood scoop function on a car like that where the air all around the nose is scrambled up?