These days a "crate" engine jsut means somebody rebuilt it. So not sure what all you're working with. As in, your car was a straight six and you'll be needing all the V8 stuff or it's a 289/302 with a tired engine getting replaced. It makes a difference on what advice you need and will get.
If the engine is a 1981 or newer, it is a 50 ounce imbalance engine. You will need a 50 ounce imbalance flexplate/flywheel (depending on what transmission you will use) and a matching harmonic balancer. The rest you could swap on 289 parts to put back together.
If your "crate" engine has a water pump already, it should be the reverse rotation one for a 1983 serpentine belt setup. Two ways to deal with that. Go with a serpentine belt setup or got with the original v-belt setup. If V-belt (rather easier and cheaper) you'll need to change timing covers to match the vintage style water pump. As the 1983's still had mechanical fuel pumps you should be OK there. But an '83 5.0 Mustang had the oil dipstick in the driver's side of the block. You can't use that with a 68 style oil pan. So you will need to either drill the timing cover for a dipstick or get one correct for your car which have the dipstick provision already.
Lots of folks have done 5.0 swaps, there's some stuff to it but nothing you can't overcome with the right mix of parts. It would help us advise you if we knew a bit more about your new engine, the old engine (if you even had one), what transmission you plan to use, and what flavor of "restomod" you want to end up with under your hood. IE, a 5.0 disguised as vintage, a "day 2" style car, a regular warmed up carbureted 5.0, full on modern EFI, or what.