I think you're right on that, Jerry. And even if it was in production, the Chevy trucks used the Eaton sourced axle, starting in '47. For the most part, the 3/4 tons used the 4.56, 1 ton used 5.13, although the 5.13 was optional in the 3/4, and later 1 tons could be optioned with the 4.56. Around '67-'68 was when the 4.11 gear was offered with the automatic, and there is a very rare 3.55 (I've only seen 1 myself) offered in '72.
Now if you was wanting to install a Dana 60, it can be done. You'll want one from a Dodge 3/4 or 1 ton van (the width is very close, GM and ford might work, too). Use caution, though, as many of them, especially from the mid '80s-up, are semi-float. Many of the Dodge 60s come with 3.55 gears, I'll bet that there's 3.73s out there, too.
