Are you looking to make this truck "better than stock" or just through in the cheapest set-up you can find.
Cheapest V-8 swap would be to find a used, running small block, spend about a $500 on incidentals,
another $600 on conversion pieces and 750.00~ 1000.00 on labor to a shop to R&R the motor. I doubt anyone will give you a turn-key set up for that much but they would probably pull the old motor, clean
up the frame, cut off the old mounts, and set in the V-8 and tranny. You'd probably be doing the wiring, fuel and coolant lines yourself. Then you'd still need to send it out for driveshafts and exhaust.
It will be faster for sure...but better? Probably not better off road overall. Better in sand and mud but
not in the rocks or in the slow going.
To make it better set aside ten grand. Injected motor, either an automatic with serious transfer case
options (orion, tcase doubler,etc.) or a granny gear manual. Upgrade the cooling, gages. Longfields and little wider stance is nice.