Help with a bedside issue....

[UGAK5]

I am doing a full restoration on my 1972 Blazer CST. I replaced the rear bedsides with aftermarket, but they are not drilled for the hardtop/softtop nor do they have the captured nuts under the bedrail for the single wall hardtop (which is what I have).

So, heres the obscure part question - - does anyone know of a good replacement captured nut to weld under the bed rail?

The factory one is a rectangular piece that allows the nut to slide around a bit inside a track to insure you can align everything.

I know I could just use a regular nut/washer, but since this is a CST truck, I do plan on replacing the inner upholstered panels that go inside the bed, so I wont have access to the underside of the bed rails easily.

Appreciate any help or alternative ideas that others may have done - Thanks!