I own an Upton 7/8 hybrid. IMO Upton makes fine basses. Their lams compare well with Shens or other decent modern lams. Uptons probably cost somewhat more - I'm not sure how much, and you would have to determine whether any premium is worth it.
The major difference you will immediately perceive compared to Kays/Engles is the neck. Many people decry the neck profile on Kays/Engles. I also own an Engle. The neck is narrower than the Upton, but I've never had a problem with it, and have no difficulty switching back and forth.
Realize that time is not necessarily kind to old inexpensive basses. As a very general rule, most newer plys will be more solid than many/most old plys. Some people criticize the build/sound of Engles, but I have not personally perceived any issue in those areas. (Some people differ - but my personal experience is that I really like Kays, but have not found one that outplays my Engle - for at least 3x the price. YMMV.)
One issue - which may or may not matter to you, is that many Upton lams are finished in a basic brown, which is not the most appealing finish IMO. But looks should fall so far behind sound and feel that it is essentially a non-issue.
BG/oldtime is my wheelhouse. An Upton standard strung w/ guts (my preferred string) or Spiros (many others' fave) would do pretty much anything any BGer would want to do.