U.S-spec Pantera GTS (one of 138 built both '73 and '74) are a decal version of the std. U.S. Pantera. Yours has the uncommon 'bumble-bee' paint scheme. There is a second variant sold only in Europe directly by DeTomaso, where the std narrow-body Pantera is the 'GTS'. That car could be optioned up to a GTS/Gr-3 Pantera with all sorts of things never sold in the U.S by Ford.
On the POCA Web site are two Gr-3 catalogues listing the possible legal add-ons once available. A GTS/Gr-3 was a potent club-racer and some were further upgraded for International FIA road-racing and hill climb events, back in the day. A few U.S. versions have received some of the Gr-3 add-ons over the last 45 years; you might check for their presence.