Frame comparisons for rust repair

[DanMcG]

Sooo I pulled the box off my 77 K10 short bed only to find the top flange of the frame rail rusted through right above the shock, a good size section of it anyways, at least a few square inches.
If I was to look for a replacement frame rail section, what would fit besides another k10? C10? c-k 20? I'm pretty sure k5's wouldn't work? I'd want a section from near the cab to bumper.

 

[bucket]

If it's just along the top of the rail, you could have a piece of steel bent and then section it in.

Other than that, you will be looking for a 10 or 20 pickup frame. But keep in mind there were different thicknesses used for the frames.