I thought that that was a custom option. Was it hard to fabricate? Did it work without leaking? It does look cool. I have a 70 fk5 barracuda that originally came with a bench seat.
Are you talking the T-roof?
I would imagine that it's doable but I would watch out for the rigidity of the car after a t-roof is put on. Even though there is that strip of metal that acts as structure, the roof section is none the less weakened. We used to have a couple of t- roof Trans Ams. On the '81 we had (last year of the 2nd gen firebird with t-roof thus supposedly with less issues to deal with.) the center section was starting to tear (the part between the glass t-roof panels) as we had a steep driveway and the frame of the car would twist when we went in the driveway at an angle. Flat driveways probably didn't put as much stress on the t roof section. We didn't have issues with leaking. I don't know about Cordoba t-roofs if they leaked or not. Looks like this guy did a custom fab, not a dealer option to my knowledge.
One friend of mine about 20 years ago had a 80's Malibu wagon and a '70s T-Bird that he got the Sawzall out and made them both into Targa top cars. He cut out the section over the front seats then made a tonneau roof section with vinyl and snaps. Look very cool on both, moreso the T-Bird as it was real classy since it was white with a white interior. These may have been full frame cars (as opposed to E-bodies which are uni-body design) so there was more rigidity to start with. Sorta like you wouldn't turn a hard top e-body into a convertible.