A spot blaster would work great on the top of the door, and it would work on the cab to see how bad the pillar is. The one from harbor freight should hold up long enough for hobby use. I use Black Diamond coal slag media from Tractor Supply, the finer grit version. Epoxy primer over clean blasted metal will prevent rust from coming back better than other types of primer. I use SPI epoxy, it sands well, has excellent adhesion and corrosion resistance, can be painted over, and can be brushed on for small touch up areas if you don't have spray equipment.
I replaced the roof skin and drip rails on my current project, you can see the posts about the roof starting on page 7. This was worst case scenario, yours doesn't look as bad but this will show how to fix it if it's worse than it looks from your pic.
http://67-72chevytrucks.com/vboard/s...=784498&page=7
Spot blaster:
https://www.harborfreight.com/21-oz-...CABEgI9K_D_BwE
Coal slag:
https://www.tractorsupply.com/tsc/pr...ting-abrasives
Epoxy primer:
https://www.southernpolyurethanes.com/epoxy-primer