'76 400 in a '73 duster

9" drag radials will fit, and there have been a lot of fast cars get their E.T. from 'em.
I'll also say if my truck would have had any cam and those 4.11's, I'd got into 13's for sure. Your in a Duster, so I think 12's is what I'd expect. How far into 12's, well, you'll have to show us!!!