It's really great to read so many information about this , guys, thank you
I bring you back what I know:
The Yellow TS challenge #12 (1992 Italian GT series #9) was the first convert ,when the official challenge did not exist ,and the 348 did not run in any championship. It's a TS because the owner bought it so from SA.MO.CAR in Rome, and since he was already a pilot in other categories and with other cars, he wanted to make the "madness" of converting his 348 Ts into a racing car.
I have the roll-bar assembly photos, fitted and welded in the car, slightly different from what was then the definitive one of the KIT sold by ferrari in 1993. (and in some photos in the race, you can notice the sloping cross otherwise)
Coming to, how many TS were built in italy:
We start from the fact that as specified by @ Robin348c, the first 348challenge were the Italian ones, and were not cars produced by Ferrari in racing mood, but it was the 348 base, which was equipped with official Ferrari kits when owner GENTLEMAN, or TEAM wanted to participate to the challenge championship.
The Kit was included in the total cost of the season along with various gadgets (bags, helmet, jacket etc.).
You can still see at today,the registration form to be completed on the last page of the "technical regulations" 348challenge booklet.
The number of 348 TS challenges, in 1993 I think it was 5/6 (1993 Italian championship, the very first).
I knew from former 348ch Drivers, who in 1993, just released the news of the 348challenge championship, many GENTLEMAN-born riders and also official TEAMs then wanted to participate. But TB cars were "over" and those who did not want to wait for TBs to deliver, and they took TSs to start competing right away, quickly.
Rumors say that the TS for obvious reasons was not good and fast, initially, like TBs. This is due to obvious technical speeches, tilt twist and weight.
Many also tried absurd solutions, such as welding hard-top ...
However, this was denied the following year, because winning the championship was the 348 TS challenge # 22 led by Sandro Malucelli.
(Visible online photo)
This is what I know, and I can tell you to this day.
TS challenges did little at first, then in the German and US championships, increased in the following years.