My uncle Wesley had a modded Chevy six back in the day, and my friends wife has one in a 50 Impala with aftermarket intake. That being said, another friend had a 69? Chevelle, 396, 4 speed, 850 cfm Holley, ran 18's in the quarter. You just don't know...
The chevelle should've been faster than that. Maybe he didn't know how to tune his combo. My stock 74 duster with a /6 ran low 17's. Depends on what else was done, that 850 could've been to much carburetor, I've seen it before