$100 is a very good price for a set of 15” road wheels!
The ‘79/80 Gran Fury is a R-body which would have the 11¾” front brake rotors (and caliper brackets). The rotors can be gotten new, but the brake caliper brackets and spindle attaching bolts are what you want. The attaching bolts are longer and important to save.
The spindles are the same as FMJ. Not real important to pick up – but they are getting more difficult to find and a part that does get damaged (curbs, etc. as well as wheel bearing failures).
If the car has 11” rear brakes – that would also be nice to pick up. I think about 1 of every 4 R body has 11” drum brakes on it. If not to use, then as a good selling item (to the older muscle car fanatics).
If in good condition, the front upper control arm alignment/adjustment bolts/nuts are also getting hard to find.
The late B and R-body has a 28” wide radiator (the widest in FMJ’s is 26”) – but are not a direct bolt in to FMJ’s (can with some minor mods). If radiator is good and a 2 or a 3-core, I would grab it.
Some dash/interior parts are the same as J-body’s but not sure how much. I'm not a J-body expert.
A lot of the underhood electrical parts are the same as your other cars (voltage regulators, and so forth) so getting some good (ie: non-Chinese) spare parts might be a good idea.
If car has cruise control and if one of your cars is missing cruise, this would be a good source for parts. The servo fender bracket will not work on FMJ’s though – but everything else should.
If car was a 4-bbl (318 or 360), then grab the throttle cable and kickdown linkage and brackets (rear intake bracket, and all parts from carburetor to transmission, including pivots and brackets).
If car was a 4-bbl, I’m looking a decent air cleaner assembly (with a computer attached to it, or not).
BudW