Just dragged home: 1966 K20 barn find w/o the barn

[Clanky]

Hello All!
It's been a while since I was on here. At the time I had a '71 GMC K1500 that I fell into but it was always a little too new, had those new fangled disc brakes and whatnot.
I came across a 1966 Chevy K20 on Craigslist here in NM that needed a 'little' work. It's a barn find that never lived in a barn. I ended up trading the guy for the truck for around $600, so I'm it into pretty good.....so far.
Anyway, here are some pics. As you can see it needs a 'little' work. It has a '64 bed on it as it was once a farm truck with a flatbed. Does anyone know whether or not the only difference in the '66 bed are the reverse lights?
Can you tell me how I can figure out if the engine, transmission and transfer case are all original to the truck? My goal to keep it all original, so I'll be shopping for lots of stuff pretty soon.
One other question, the wheels on my truck have the 'nubs' for the hub caps. Is that correct for '66? Not the clips?
Thanks much and take care,
Karl Franklin