Factory paint sequence

[TLea]

Trying to make this restoration (66 C20 long bed stepside) as accurate as possible. Painting the bed this is what I understand so far please correct me if I'm off.

1. Bed is assembled, sides/front/rear crossmember/tailgate
2. Painted wood is installed then masked off
3. Bed is painted

Here are questions,
1. What is on sheetmetal at the point it is assembled? Primer? What color?
2. Were rear fenders installed when bed painted?
3. Any further treatment to underside of bed? IE: sound deadner/blackout?
or looking underneath after paint would I see mixture of primer, bottom of painted boards and body color overspray?

I know this is a lot but thank you