Pop-riveted flares are standard for that year.
It appears that the engine is not original to that car. Generally, in the Pantera world, few people care about matching engine numbers since most Panteras have been modified.
To get a better idea of what a GTS looks like, visit: http://www.pim.net/gts826.html to view a '74 for sale by Pantera International. Your bumpers will be the bumperette variety as it is a '72 and a European edition, I assume, and not the full bumpers as in the above American example.
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