Something's fishy.

A 264 would have a VIN starting with YV1BX. The engine code '45' indicates a B21F was installed at the factory.

So I'm not clear on why you think this was originally a V-6 car.

Furthermore, a 1982 V-6 car would have been badged GLE, not GL.

In 1980-81, there were some YV1BX cars that came from the factory with B21F, no one knows why, but 1982 is out of this range, anyhow.
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'73 142, '75 242, '75 245, '80 245, '83 244, '86 244, '87 745T, 92 244 (for sale)

I helped a friend at a shop that did quite a few of these. Once the old B27F started to go bad, it would need its cams replaced. The cams would apparently go flat, i.e. wear out. Valve clatter and reduced performance were the result. Heads were always getting rebuilt on these- to the tune of about $800 per side.
A good used 1976-80 B21F engine cost half that much. Then you had a car with a decent reliable engine, and all the "GL" stuff, power windows, locks, nice seats, the fancier 4-headlight grill and big taillights. Usually alloy wheels as well.
We had no trouble at the time (this is 1989-1992 or so) finding good running 240DL rustbucket donor cars, as well as 1980-something 264GL's in need of motor work. Even did a few 240 diesel conversions. Those required changing the tank and the fuel lines, but still quite possible to switch to the reliable gas engine.

Sounds like this one is more of a hack job but you hit the nail on the head: it's a conversion car.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 234K, '82 245T/M46-182K, '89 244DL/AW70- 212K Not too distant past: 86 244DL 215K, 87 244DL 239K, 88 744GLE 233K, 88 244GL 147K, 91 244 183K