Can't believe that no one has responded in all this time since your post. Hopefully, you've gone to a more informative site and gotten an answer. I'm new to this forum, and couldn't help to respond just in case you are still stuck.
I'm very familiar with resto work on Fiats, and suggest that any part that was originally installed on your car can be replaced. It is just a matter of getting the replacement, and persistance. Stay away from a shop that will not guaruntee its work! Just because they "install" tops doesn't mean they know how to do it correctly. I had a boss tell me once he'd be willing to do anything for a buck, so long as it was legal.
Replacing a metal part is usually better than welding broken pieces together. Welding can change the shape, length, and tensil of the part. Only use the welding method if you can't find a replacement. I'll betcha you can find a whole, intact vert frame at your local junkyard for a pittance of the cost of the OEM replacement piece. Just the persistance to find the right yard with the right car.
I replaced the top on my Fiat by myself. I was able to fiberglass a rust area on a metal part, as it only needed to be a specific shape, not structural strength. That, and the replacement part was pricy. Except for the fiberglass repair, the entire top was done in an afternoon.
__________________ daughter owns '00 GT, bone stock, black on black, rag top
dad services and maintains, and researches mods | 
