3.9 V6

The ‘91 was the last year of TBI, ‘92 was first year of MPI Magnum 3.9 with a huge increase in performance - so no it does not have newer efi.
It would be good in a duster. It’s just as much work & $ as putting in a V8 so I wouldn’t bother with swapping it in something else.
The Magnum 3.9s have a lot of torque for a V6, just a touch lower HP than Jeep 4.0 but much more torque.
Not sure there is much available for increasing performance and the Magnum really need a better intake manifold.