To my understanding, it would be the grey rubber mats in front of each seat, judging from my early '67 250 SL. Carpet on the tunnel, door sills, rear shelf and well. The mats originally were on top of a jute pad, which now can be mimicked with the proper thickness of quality felt. (Don't know what that thickness is for sure)
John Lewenauer
1967 Early 250 SL Red/Caviar, Manual