Bdave is it an auto or Manual? Early XB GT's were fitted with Top Loaders and mid to later XB's all had single rail boxes. I am sure the Radiator support panel is thicker on the GT compared to the GS, 500, Fairmontís. I know on the earlier GT Falcons it also had a number stamped in there as well which should correspond with the JJ 33 on the Compliance plate.
The Mrs and I went to have a look at a XB GT last year, which was going for 5,500. A friend of our who had an XB sold his for 7,000 and it was a little rusty. He sold it because he could not keep both that and his XY GT.
I will try and contact him tomorrow and get more details on the XB GT's.
Used to be Mustang1966coupe.
66 Silver Frost Mustang 289 Windsor
71 XY GS Fairmont in Bronze Wine 302 Windsor
92 EB XR8 302 Windsor
Sure do love those Windsors