Radiator for 1988 Mitsubishi Mighty Max?

[FMS88]

Glad to see PartLimit was legit enough to refund your payment. Try looking for the Spectra Premium CU758. On this site it looks like the CU188 and the cross-reference P/Ns include that of the '88 MM with the G54b.
https://www.autoanything.com/coolers...iABEgJYqvD_BwE
Autoanything may be as flaky as PartLimit, but there might be other reputable sites that have the CU758.

Although I don't like promoting O'Reilly's due to past negative experiences, I found this on their website:
https://www.oreillyauto.com/detail/c...e-ram-50?pos=2
Doesn't indicate availability and I've never heard of Murray Radiators. Reviews look underwhelming.

If new radiators aren't available, any used ones at a local wrecking yard that you can pull and have a radiator shop test for flow and leaks? If it failed you could at least return it to the yard as defective.