yes, it is tough enough for cyclocross-in fact a lot of cyclocross frame sets were made using 531 Reynolds. It would not be ideal for that sport because cyclocross bikes generally have cantilever brakes for better mud clearance and steeper frame geometry, But if the conditions were dry and you just wanted to sample the sport, a bike like that wouldnt hold back a beginner too much -- if it was not muddy.

But i think it would make a really neat gravel machine and should be able to handle 35c tires , maybe 38's

i rode my first cyclocross race years ago on a borrowed, beat up old Schwinn LeTour because it would handle a semi wide knobby hybrid tire we had at a bike shop i used to work at. There was no mud clearance after squeezing a hybrid tire on with the sidepull brakes, - but it was a dry day and the bike did fine. i drew a few good natured laughs and snickers at the budget grade makeshift machinery i was using, but i couldnt afford a dedicated cyclocross rig


regarding the integrity of the people in the sales forum --- there are guys in here that i have never met face to face, but i would trust them with a high dollar bicycle purchase . I have never been burned buying things through this forum . Something i cant say about ebay.
There might come a time it happens, sure, no system is perfect, but the guys i have bought components from have all been very straight up. In addition to that Colnago, i have purchased a nice Paramount, several wheelsets , complete groupsets for my vintage builds- and more.