To expand on Kranky’s information,
FIA Cobras utilized OR & CR aluminum Girling calipers, USRRC cats ran stock specification calipers. FIA cars had purpose built dash panels void of glove boxes and larger than stock instruments laid out inline with aircraft switches, USRRC cars typically used street dash panels, gauges, switchgear and a glove box. There were later USRRC cars that had dashes solidarity to the FIA cars. Not all of the FIA cars received trunk lid dimples and none of the USRRC cars had them. Early USRRC cars didn’t have an oil cooler chin scoop. Differential coolers on USRRC cars were mechanically driven off of the differential, FIA cars used an electric pump. FIA cars used a purpose built aircraft style wiring harness, USRRC cars used a standard street harness with additional circuits wired in as needed. USRRC and FIA cars tended to utilize 6.5 & 8.5 x 15 magnesium wheels, there were variants of both that had 7.5 x 15 rear magnesium wheels early on. FIA cars that had trunk lid dimples could have also had the spare tire tray modified as well. Both FIA & USRRC cars had long range fuel tanks, Fuel tank switch over valve with both electric and mechanical fuel pumps, the electric used as a booster on the reserve side of the fuel tank switchover valve. Tacos in both cars varied. As Kranky stated CSX2431 received a lot of modifications that other FIA & USRRC cars did not. At one race two FIA cars we’re equipped with the smaller drivers screen (Augusta 1964, CSX2259 & 2260). FIA car speedometers were never functional.