From what I could find...
- It's a 'V'
- Lists as what you found (2wd v6)
- The fleetside bed can swap (and if true, that might be why it was; I can imagine a stepside in good condition going for a nice piece of change) Yes, I know you're stating that more than the bed was swapped.
- You may find a VIN on the p/s frame rail, but the bed may have to be (re)moved to see it (it's on the top side, that the bed attaches to) Could try to loosen it on that side and see if you can get a USB cam or mirror in there.
Might be possible to see from Carfax, etc., if it was ever rebuild / salvage title (but costs $$ and doesn't give info on the donor truck(s), which is really what you're looking for, I think)