I'm not knowledgeable about the builder but I question the legitimacy of the tubeset decal. That's a 1988+ SLX decal and the frame looks about a decade older. I don't see any top tube brake cable tunnels. I guess there could be internal routing ports on the opposite side but there also doesn't appear to be any shift lever bosses, so it probably requires brake cable clamps. The absence of both would be strange for even a pre-1988 SLX frame, as SLX was introduced for the 1984 model year. Being Columbus' top tubeset in 1984, these frames typically had a full complement of the latest braze-ons, so their absence plus the lack of a front derailleur hanger, the presence of what appears to be only one set of bottle bosses and even the use of cable routing over the BB, makes me sceptical. The braze-on selection,seems more indicative of very late 1970s.

Fortunately, there's no BB installed, making it easy to verify if it actually is SLX. Be aware that there actually was an SLX style seat tube, a year or two prior to the introduction of the SLX tubset. Consequently, don't assume it's SLX if you seen the helical ridges on the inside of the bottom of the seat tube. Make sure to check the inside, BB ends of the down tube and chainstays too.