AMC 401 engine for my 1972 Duster
THIS IS A POOR IDEA
1.....That engine "deal" is not all that cheap.
2.....Swap like this is a LOT of work if you've never done such
3.....When you get "done" you are never "done"
4......If you decide to sell it, nobody is going to want it
If this was some odd old thing "gasser" is the popular catch all, then yeh. Drivetrain parts for these cars are plentiful.
If you want to swap that AMC into something, go find yourself an old AMC "classic" and swap 'er in there