If the engine does indeed have 70-80k on it, I'd keep the whole thing - low-mileage engines that were known good are getting kinda hard to find, if you scrap it now and later down the road you need one again chances are you'll find that people tend to want your first-born AND the keys to your kingdom for stuff that is questionable at best. Build yourself a small dolly/cradle out of 2x4 boards and some cheap HarborFreight casters, and just lay the engine on/in that and slide it into the corner of your garage.
Are you sure the trans is a T18? AFAIK those were never put behind diesels from the factory - 83-84 you could get a wide-ratio T19 (5:1 first gear, same as gassers, after that it's all close-ratio T19s. The T18 itself is the same as any other one found behind gassers usually, shouldn't be too hard or terribly expensive to source another one later if you need to - if it's not as low-mileage as the engine and you're strapped for space I'd be tempted to let it go on Craigslist, someone out there is building a rock-crawler and has a need for a bulletproof stick-shift with a creeper 1st gear. Definitely keep the bellhousing tho, as long as you have that you can use any of the Ford 4-speeds (T18, two NP435s, three T19s, and God knows what else).
T-case, keep that for sure, you have it already and it can be used behind any Ford transmission up until the ZF6. Makes good item to sell if so desired later on, fixed rear yoke is a good thing and you don't generally get that in the next-newer model t-case unless you build one like that yourself.
Driveshafts, I'd pull those and stand them up in the corner, or hang them off the rafters - junkyards generally destroy the shafts when they position the trucks so finding straight ones on the cheap can be quite an ordeal. If they end up too long for your next project shortening them is cheap and quick, and if they are too short retubing a shaft is usually still cheaper than having one built from scratch.
If she has a gauge cluster with a factory tach, keep that as well, even if you don't need it I bet at any given time you'll find at least one person on here who's looking for such a beast.
That should be about it. Good rust-free sheetmetal can usually bring you quite the chunk of change if you can sit on it and wait for the right buyer to show up (as opposed to the first low-balling ****** tweaker who flashes some cash your way), but I'm guessing that won't work for you - you can still throw it all on Craisglist real quick as a "you pull it" ad and see if you get any hits...
