what is the best overdrive transmission for a Duster

The adapter plate would be the biggest expenditure. I think they are in the 500 dollar neighborhood. Then of course there's the cross member mod and making the drive shaft work. Far as what they came out of....

The THM200-4R can be found in the following vehicles:

• 1981-90 B-Bodies, Impala, Caprice, Delta 88, LeSabre, (83-86) Parisienne, and wagons
• 1981-84 C-Bodies, Electra, 98, (82-84) DeVille & Fleetwood Broughams
• 1984-88 G-Bodies and Pontiac Grand Prix, GMC Caballero, El Camino, Chevrolet Monte Carlo, Oldsmobile Cutlass Supreme, Regal
• 1985-90 D-Bodies Cadillac Fleetwood Brougham & Brougham
• 1981 Pontiac Firebird (with 301cid engine, non-turbo)
• 1989 Pontiac Firebird Trans Am Indy Pace car (with Buick V6 and a Turbocharger)