If your alternator is failing you likely will see the battery light flicker or turn on while you are driving. Your gage might be the problem as well. Before I went to crazy I’d wire in a cheap digital voltage gage and see if its readout matches...
Maybe I missed mention of it but have you baselined the rest of your truck? Valve
Clearance, timing, compression check, intake and exhaust manifold gaskets and seals, and vacuum leaks?
These days getting a spare 60 as a parts donor is a valuable investment. I’ve got a super rusty 62 that’s basically holding spares for trim and glass etc.
I scored the bar where I wanted the bends with a grinder, bent where I needed and then welded the score lines. I used the two cross bars to stiffen them even more. They turned out pretty sturdy