It's a re-paint, that's a start. He and others sellers have been selling that brand for a number of years now on e-bay. Some have a tubing sticker bt in many cases the tubing is only implied, stated or not. There's a stash of Guerciottis somewhere back in the old county. The beauty is, that on account of Guercotti's no account of exact history, record keeping, tractability in builder source, it's an ideal candidate for selling as NOS, repainted as stated or not... or the like.
It's not an SLX frame and can't possibly be a TSX. The years alone belie these possibilities as the man stated the spacing's been spread which is written testiment.
Theoretically narrow spacing could possibly exist on an SLX frame, statisically a virtual near impossibilty given the year. All this simply judging by his words, the year/spacing.
The fork crown; that design wasn't used on many SLX frames which more often than not had semi-sloping. SL frames used mostly the flat, "traditional" crowns as did both Aelle, Chromor & Gara. The crown's cap been replaced too I suppose. Campy bits are standard issue or can be retrofitted, not at all telling.
Checking for the riffling would show its being an SLX, it would not distinguish an SL from the others. Seat post diameter ID, best indicated by what S.Post fits can tell you that it's SL. Bear it mind that the majority of more modern chromoly bikes use 27.2 so why not use one off another bike to check if not, you would oherwise need to measure carefully with a caliper. I've little confidence that it'll be easily done without an actual seat post. ODs on posts are easier to meas. than IDs of tubes. Calipers can be tricky. Remember, only a few fractions (.2 mils) at times can be a dec. factor even when meas. exactly, a frame from one company could've chosen a different seat tube or swedged size than another. 27.2 shows it's SL whith fair accuracy. If it's considerably narrower, it's most likely not. I hate using that criterea; too many exceptions due to chosen bits of tube irrespective of what the bike was sold as, often a tube or so would be dif. which was the BUILDER'S choice.
It's a nice frame, worh every penny; The OE paint was often not the greatest on many Italian bikes. It's got nice work, it's not typical of Chromor but it could be. My bet is...it's Aelle. Those who ride such framed bikes describe them as "sweet".
Chromors are fine too, those I've ridden and can't tell the difference. SL speaks for itself. You were wise to buy the bike and not buy into the notion that tubing model is the be all and end all. Leave that for big fat showoffs such as myself.