Ditto on the weld it up point, but also depends on whether you're wanting to keep the original patina look or are planning to repaint. Keeping it original paint otherwise would be challenging if you weld the filler hole shut. Could be painted to kinda sorta match though. Another option is a dummy chrome (or rusted) or painted filler neck cap with a boxed neck cover inside the bed (like a 69-72 NL2 RPO). Just gotta remember to not fill er up
As for pic 1, my first thought was a horizontal camper shock, but I don't think that's correct because there's no pass-thru at the front of the bed sheetmetal. So, hmm, dunno.