Check with referee but I think the rules are that you must swap in the same year or newer engine.
So you need a '99 V8 or up.
Best way to do it is by getting an Explorer with V8, could be rusted out or have body damage(rolled) so you can get it at a good price.
You need the engine/trans, wiring harness and computer for the swap so...........
May want the rear axle as well, if yours is a 7.5", you want an 8.8" with a V8
And because it is '99 and up you will need the ignition key cylinder swapped into your steering column, you need to use the PATS keys for new computer to work so make sure you get all the keys they have for the explorer.
Mercury Mountaineer will work as donor vehicle, very similar to Explorer
Good read here on aspects of this swap: http://www.therangerstation.com/Maga..._v8_swap.shtml