Big Block seems to slow

A "good running" 361 with a 4bbl and dual exhaust should be no slouch in a Duster. With a factory 2bbl and single exhaust they listed at 265 hp and 4bbl at 305 hp. I mean, it's not a 440 either. If it feels like 18 seconds, you are in slant six territory and I'd suggest giving the 361 a compression test, tune, make sure the throttle is going all the way open (all 4 barrells). Start with those things...