Bertone museum?
If Turin/Torino is within the scope of possible places to visit - and, if you can actually verify in writing that they'll open it up for you, I thought this was a highlight of my only trip to Italy, about 10 years ago, when my wife and I joined the "Car Guy Tour". Apparently, even w/ documentation, you may still be SOL when you appear at the gates. This
is Italy, after all. But I'd still try - what's the worst they can do to you? Actually, being Italy, I'll retract that question.
By virtue of the tour, we were able to visit an unbelievable array of factories, museums, design/styling houses, etc. I assume it would have been next to impossible as an individual to replicate this experience. We were also extremely fortunate in being able to talk our way onto the Ferrari factory tour, due to my wife conversing extensively with the woman who was the organizing/marketing coordinator at Ferrari, earlier, at lunch. She must have just
assumed we had our letter. Being part of a group (several of whom had astronomically scaled egos and demonstrated a level of rude behavior that would put a drunk sailor to shame) was obviously an immense advantage.
I mention Bertone, specifically, because seeing the prototypes that I absorbed as a youngster through the car mag. images was absolutely surreal - and wonderful. Bertone has always been a favorite designer of mine, and with a Giulia Sprint GT in my barn, the place just resonated with me. I seem to recall that you may have one of these, too..
Anyway, Pininfarina was my second favorite locale, but if it could only be one..
Good Luck.
-----
Oops. Almost forgot - two cr*ppy quality, teaser pics, shot straight out of the photo album. It was '99, incidentally.
Museum -
Corvair styling exercise - (second car on right, in above image):