Hope I'm not too late, but I might as well chime in.
Stock axles will be a D44 open knuckle disc brake front, with spicer external lockouts (with the big plastic knob, if stock).
Rear axle is most likely the Eaton H052, but there is a very small chance it could be a FF D60. If the glove box option sticker is intact, look for any RPO codes that start with a G8 and then another number. I forget what their respective numbers are, but if it has the Eaton axle, it could have a factory Detroit locker (will be called a No-Spin on the sticker, there will also be another sticker for this somewhere inside the truck, like on the roof or behind the seat). If it has the D60 it could have a power lock posi, which would also be indicated on the sticker.
If it has a 400 small block it isn't stock. Check the VIN. If it's an original 4x4, the vin should start with a K, followed by a S or an E. If it has the S, that means the truck originally had a straight six, the E means V8. Any optional engine would be listed on the sticker, and 90% of these got the 350. 400 was not an option in this generation of truck. The 402 big block was only available in 2wd trucks in these years, so if it is a BB that isn't stock either (but would be a nice find).
Tranny and transfer should be TH350 and NP205.
Other than that, check for rot in the frame behind the rear spring hangers, the rockers and cab corners, firewall, and above the windshield. If it has really bad windshield rust be on the lookout for a new cab.
Good luck!
EDIT: here is the sticker that was originally put inside the cab at the factory if the Detroit Locker was installed. I have seen 3 of them, 2 on the roof of the cab between the visors, and one behind the seat and next to the gas tank.
