Looks nice but I would need to see more pics. But also way far away from me and in a foreign country so...
All '73 -'75 GS's I have ever seen were Century Custom Sport Coupes, not-a-one with the formal roofline like this one.
I believe you could get a 455 in this body style, I remember seeing one in a Colorado junkyard back in 89' or 90' and it was wearing '455' badges on the front fenders above the marker lights. It probably had a U code in the vin and it looked very original. Larry.
I owned that car for awhile, bought it from the original owner under 100k very nice car , kid put a 3.42 posi in it. I was shocked when he advertised it as a gran sport, it’s a Factory numbers 455 car I did the driver seat and rear seat bottom. It’s clean but needs work. Original vinyl shredding etc.. I haven’t seen it in years but he lives in my town and I don’t think he drives it much. He’s a good kid just not a real Buick guy. I have pics of when I got it and some repairs done.