It seems to me that the Euro GTS have a more powerful engine, 330 or 350 hp vs 270 for the US GTS. Am I wrong?
Others mentioned 'custom order': to me the value of the Euro GTS is, such Panteras could be factory ordered with any or all of the factory Gr-3 enhancements intended for international club-level racing and hill-climbing. GR-4 parts were also possible across the counter, both for non-factory installation. The Supplemental Parts List for the '71-up Euro GTS is 16 pgs long. NONE were available in the U.S. until after Ford departed the scene.
With a Euro-GTS, it was like Christmas morning as you looked at what was 'uncommon' on a Pantera! The factory parts available included Weber intakes, (likely) Boss heads and cams, factory Holley 4 bbls on aluminum intakes and freer-flowing exhaust systems.Even stereos were factory-available. Handling updates were also listed as well as custom ZF gear ratios, 10" magnesium rear wheels and far bigger tires with fender flares.
Nowadays- 48 years later, dependable 600 bhp Panteras with 6-speed ZFs, giant wheels & tires and with enhancements DeTomaso and Dallara never dreamed of are commonly available. Bring money and your dreams!