I have this Piero Zurino which i believe is a Losa frame but can´t be 100% sure because the lettering on the seatstay caps is a little different from all the losa frames i have seen. It has chromed seat/chain stays, bb shell and seat lug, also fork. Campagnolo dropouts and when i bought it had columbus sl decals that fell apart the first time i washed it. It is also a very light frame (around 1.6kg, fork around 0.68g).
I know Giovanni Losa made frames for different brands, and Piero zurino is/was a swiss bike shop with made to order bikes, it may or not be a losa frame but it is, i believe, a quality frame. I haven ridden it for some time and it is really fast , light and nervous...
I'm in no way qualified to comment on a rarity such as this, but it is so lovely that I had to stick my oar in.
If I saw that up for sale, I wouldn't be surprised to see a price tag of £500 on it. A lot depends on just how rare it is: I haven't followed up your links or done any digging myself, but I can smell the quality from here.
Despite what you may have read elsewhere, there is a huge wealth of knowledge on LFGSS.com and they love a classic Italian; you'll find "how much" and "what's this" threads there and I think this would generate a lot of interest.