they may have used a fibreglass shell or one of the kit cars, but following the plot line of the series, it is based in roswell new mexico, about aliens, and obviously close to groom lake, it is pretty much assumed from the series that it is an ex military vehicle from the base, as for the modded parts, could just be because Max was in his early 20's, alien, adopted family not much money, and in the show they went to a scrap/junk yard to get parts for a vento so maybe he needed parts to fix up his jeep and pulled off anything that looks right to bolt on lol anyway check out the Jago Jeep kit car if ur in uk its a good base second hand. it is based on mk2 ford escort running gear tho. cheeper than the jeep wrangler as a start