Plymouth launched the Duster for 1970 as the A-body youth-market sport coupe — Valiant chassis underneath, all-new fastback roof line + bodysides. The Duster sold immediately on its appearance + low base price + the eyeball-catching Duster 340 high-perf trim layered on top. ~217,000 built in 1970 across all engines, making it one of Chrysler's volume successes that year.
Body code prefix: VL (Plymouth A-body fastback). VL21 = base coupe; VL29 = the Duster 340 with the high-perf trim package.
Dodge didn't get an equivalent until 1971 (the Demon, separate entry). Through 1970 the Duster had the youth fastback A-body to itself.