I can't stop thinking about the build either. I am 6'2" and have a 34 inch inseam. I fit fine in the Crusader which is essentially the same size as the Abarth. I haven't seen one in person so I don't know for sure. But, I think that fitting will be fine.
The person that made the molds tells me that there is room for most drivetrains. He tells me that a V8 will fit. I'm not sure if he meant longitudinally or transversely.
I have used the Porsche glass in several builds. I have a frame that I built for Miata parts that I test fit an old fiberglass body to and placed the glass to see how it looks. Attached is a picture of that.
There have been several of the Abarths that I've found pictures of that have a low windscreen and one that I found that had a fiberglass insert that fit to the stock windshield surround and a short plastic wind screen was attached to. I'm thinking that a fiberglass insert that fit to the stock windshield surround and then to the Porsche glass would be feasible. I see that as easily being removable so depending where it was driven you could switch from a DOT windshield to a windscreen.
The third option is to make a mold for a glass windshield that fit the stock surround and have it custom made. I'm thinking a lower speedster version for this. About 12-14 inches high.
My Beck lister with the Porsche glass (I sold this car some time ago)