hola! first, is it a 2.0 or a 2.5, as they are very different propositions.
I would say assume the worst at all times with a old GTV, until you've fine toothcombed it.
Rust - wheel arches and sills (check under the side skirt thingy. There's usually a nice collection waiting to say hi!). They rust on the jacking points and the base of the A-post (pray it doesn't have a sunroof - they're the worst). They rust by the battery box in the boot, too. Lift the plastic rain gutters too, sometime they hide...rust.
Want some more rust? Ok, so check the bottoms of the doors. That's if the doors still have a bottom...
Check everywhere for filler and bodged repairs.
Oh, one of the classic mags had a feature about buying a GTV only last week or so ago, but I can;r remember which mag it is now.
mechanically, the same as any Alfetta series car; dodgy donuts that may go pop, rear calipers sieze through lack of use, handbrake bound to need adjustment, gear box may be sloppy because linkage deteriorates.
That aside, they're lovely. In red. With a V6. And low mileage. And no rust. And...I need to sit for a bit now
let us know how you get on