I know, my friend used to race a 302 Granada on the oval tracks and his class required stock unported heads and a stock 2 barrel carb. He used 351w marine heads and a 500 cfm 2150 off a 429. They had Ford part numbers so the tech guys were happy. A 351m from a 70's truck had about a 350 cfm carb. The cfm recommendations in the carb catalogs don't jive with my experience. I built a 302 with an RV style cam, stock fox headers with the dents removed, and an 85 Mustang GT intake manifold for a Cougar sedan I had. The chart said I needed about 450 cfm, the new Holley about that size is big bucks so I bought and rebuilt a used 390 cfm. It ran good- I thought- until I swapped the 600 off my Mustang. 390 is a lot closer to 450 than 600 is but the engine liked the 600 a lot better.