Looks like a 57-60 panel roof/ rear section grafted on and a 66 bed welded to the cab. Looks like a ton of work and it really didn't fit that well IMHO.
Not a unibody, the bed body line is straight instead of tapering downward. Would of been easier on a uni for sure.
I've been wondering about this conversion for a while. Glad someone tried it. Uni would have looked better. Maybe if this one was slammed it would work better.