The studs are called weld studs, but if you weren't lucky enough to save enough of those plastic clips that hold the trim on I wouldn't bother, and grind/twist the ones on the cab off.A tape pinstripe will be your friend here. Hire a stripe guy, it'll be worth it.
The last of the plastic do dads I bought were like $11 or 12 each, and as you know there are a bunch of them. I believe there is a plastics company repro-ing them now, out of the Tampa area. But they are still not cheap, maybe $7 or $8 each.

If you were willing to drive to Georgia, I am reasonably sure there was a complete long bed somewhere between Illinoisey and Georgia, hell not long ago I sold one (I am a short bed guy and parted out the long bed truck) the cab and front frame stuff was all I wanted, for $200, to make a trailer out of. Florida.

As for the weld seam showing, it is likely poor surface prep, back when I was young and dumb I couldn't gas weld, no wire welder, so I brazed. That generally didn't work out well over the long haul.