As a bit more of a description. There is a small "end cap" piece of metal at the front of the rocker.

My car had the passenger front rotted out, the drivers side has an odd circle in the center.

I don't know if perhaps had some rot and got welded shut, but the rocker caps I see are advertised as E body units with "Will fit B body" and they have a welded nut in the center.

Didn't know if its used on E bodies and not B's and just needs welded shut. Or if it is used on B's and Ill have to drill a hole and weld a nut there or just buy the piece from AMD since its only around $30.

Not sure if the E-Bodies will work, I just fabricated my own pair and welded them in. Not really hard to make.

Have a look at the inner fender splash shields. Is there a hole in the shield for a fastener that would attach there? My 73 Challenger and 68 Dart both have a threaded insert in that rocker cap to attach the inner fender splash shields.

Just went out to the garage & checked my 71X the fenders have been off for 30 years,no nut/hole or anything in the front rocker end cap.