I only see the one big rubber plug on the LH side of the transmission tunnel on my car. My car has a boss in the side of the transmission that looks similar to your photo but mine has a 7/8 inch plug in that boss. Perhaps folks who know about later cars or 2+2 can say if there was a change. My owners manual tells about the fill location in the routine maintenance section
David Barnes
68 E-Type FHC