On the subject of roll-bars or roll-cages in Fiat 124 Spider, a while back, I saw a U.K. tv car program called 'Salvage Hunters : Classic Cars', (Series 7 Episode 2) I think it was on Quest Channel over here.
This episode took a Fiat 124 Spider that had already been converted for track use and did some work on it, including visiting a Co. that specialised in fabricating one-off roll-cages for a new 'cage (the aim was to make more room for the driver while still being able to raise the soft-top if needed).
They also visited a Co. that made racing harnesses (seat belts) and showed how these are made and tested.
Iirc, they also visited another specialist who showed how he fabricated a new centre console from sheet aluminum.
I don't know if you guys will be able to view this episode but it's an interesting watch, here's a (Discovery) link that might work:-
discoveryplus.com
(you might have to omit the ie/ in the above link ^^ and insert something to suit your country?)