It looks like p/n- 25515446 lists for A & G body Cutlass, but the only Olds that got p/n- 25510879 was the ‘82-‘88 J body.
Correct. For Cutlass (as well as the Olds B, C, and D, and X cars), the 80-88 bright fixed antenna is 22029243, which superseded to 22029436, which superseded to 25515446, and shows to have external threads, i.e., threaded part on the antenna. It appears that pontiac and regal G used the same. As well as Monte Carlo (non-SS). But keep in mind, the spacers are a bit different between models because of the shape of the fender tops.
All my cars have the U75 power antenna, so I hardly ever dabble in fixed antennae. I used to have all that fixed mast setup stuff brand new, but figuring I'd never use it, I sold it quite some time ago. The Cutlass nut, or part the antenna mast threads into, is p/n 10017841, superseded by 22549795 (chrome). If you want one for your Monte SS (or 3rd gen Camaro) or a black one in general, use p/n 22549794.
It sorta doesn't matter which antenna type you have, but whatever your base is, you need the corresponding antenna to match up with it. IIRC, the external threaded version is made right into the antenna mast. If you have a threaded hole in the bezel and a threaded hole in your antenna, you can still use it. Just get a correct size piece of all thread and loctite it into the antenna. BOOM!
Ironically, a single 1983 "G" listing all by itself shows a p/n of 10136718. This is a black antenna with the internal threads like the Monte SS versions. I'm not even going to ask why.
GM is weird AF sometimes. 88hurstolds and I were discussing vacuum line part number tape tags on the 307s, and my 85 442 did not come with a single tape tag on the lines. He sent me pictures of his 85 442 tags. Both cars built in Arlington. Go figure. The 87 has them everywhere. Everything but the plug wires, rotor and cap and the ECM water temp clip are original to the car. SMDH.
You can drive yourself crazy looking at all the fixed mast info for these cars.