Ugo De Rosa made custom frames through the 90s as I understand it, but some of this looks unlike anything I've seen. As you're aware, there aren't that many earlier De Rosas around, but this doesn't look like the few I've seen. That crown in particular feels wrong and I've never seen that seatstay wrap.

There are guys better versed in the earlier stuff, but I wouldn't get my hopes up. Is the bb shell Italian?