Thanks @EnglishBob appreciate your looking into it.

Well I downloaded Irfanview, and unless there is a plugin for BUM, it no longer seems to support the format.

So I tried the other trick of renaming to BUM, where I saw the pukey green color. I loaded those into Knald as normal maps, and was able to export a height map. Seeing as these BUM maps go back to Poser 1 figures (LOL yeah, that old!) I think that is good enough for now 8-)