[dsraven]

hey, if you already have the explorer,have lots of tools and fab skills/knowledge, wanna do something not done with an AD before-at least not all the time, then I would say go for it. keep the old frame and stuff until you're done and that way you can always go back, unless you change the original mounts etc. front sheet metal will likely need to be cut up to fit over the explorer frame and suspension but, like joedoh says, you could scrounge up some from somewhere if you decide to go back to the stock frame.
grab a dimension diagram of the old truck and the newer frame. overlay the two and see what sticks out for problems. like you say, a lot of the stuff guys want in their old truck the new frame comes with. is the frame a 4x4 or a 2wd? you mentioned you could swap TO a 4x4. are you looking to lift the old truck or you just wanted the awd aspect of the 4x4 option for towing, stability etc?
I have swapped my 57 gmc on to an 04 gmc envoy awd with stock inline 6. yup, lots of custom work but I enjoy doing stuff like that and it is a challenge. is your explorer a complete running unit or just a bare frame and running gear? for a swap like this it is always nice to start with a complete running unit because a lot of the stuff you need is there that way. it does take some space for storage though.
if you have some pics of what you have top work with that would be great for us to see.