Nice looking goat. Driven a couple like that. Also driven a judge or two.

What powertrain and mods ?

^^^^^^^^^^^ It’s a numbers matching car..has the born with drive train...and all options are on the PHS build sheet. 400 motor ,quadrajet.. Factory AC, power windows, power steering and brakes, power antenna, remote outside rear view mirror, original turbo 400 automatic trans, 3:23 posi rear, door edge guards, and it was ordered with a boxed in convertible frame, clock, and speed alert too... Has original front bucket and rear seats and door panels...original sheet metal and floors....I did put a tail light panel and trunk floor in it. Still has the original gas tank. It had the original wind sheild in it....but needed to be replaced. The car originally had wheel covers (Hub caps) ...but I like the Rally Wheels. Original code 11 Monteago Cream color...been painted a couple times. Was sold in NJ new at Rydell Pontiac...1967. The guy order the car this way....because he was towing his boat with it, Still has the markings on the rear fram rails where they welded on the tow hitch back in the day. It’s a real unmolested GTO

That sounds REAL nice. Seriously equipped for the day. Getting the convertible subframe ordered on a hardtop 2dr coupe , must be an insanely rare option.
Sounds like you got a great survivor car. I've seen a lot of goats that look good , but a lot of the ones out there are cobbled together from parts. Hard to find an original one like yours.