Don't know what motor to swap in.

That Duster can go mid twelves with a modest 360/5.9 and a manual-trans, that can still get high 20s mpg with overdrive; ask me how.

If your gonna mod the engine then the only advantage to the Magnum, to some, is the roller lifter support. As for me, I have been waiting 20 years for my 230*/ .549 lift flat tappet to expire but so far it's been a big disappointment in that.

After 24 years, I come to realize that the 360 is actually more engine than I ever needed........ but it sure was fun.