Drilling floor/rockers for seat belt mounts?

[MopaR&D]

My '70 Duster originally came with a bench seat and the two-piece shoulder and lap belts. I want to install some modern retractable 3-point belts like the ones from Wesco, etc. but they all need to have another anchor point made in the side of the rocker. Is there a way to get behind the rocker sheetmetal to weld a nut, or can you just weld one on the other side sticking out into the interior?

 

[RedFish]

A nut welded to the sheet metal isn't strong enough. It would rip right off in a accident. If you looked inside the rocker you would see a larger, thicker, steel plate welded where the retracter bolts on.
Those belts have been installed in a-bodies having bucket or bench seats. i dont know if anyone has found a good method yet.
You may find the factory anchor point is too far forward and the aftermarket retrater hits a bench seat. So instead of one more hole forward of the original you actually need two new anchor points, one forward and one further back of the original.
Good luck

 

[MopaR&D]

The original point seems like it would work as the anchor for the other end of the belt, at least when mocking up my bucket seats to where my legs are comfy (pretty far back). One more hole farther back to mount the retractor looks like it would work, I just have no idea how to get behind it.