Can't be from a B-series van, as none were factory floor-shifted.
I've seen B100s from the '80 with floor shited 833od's, length of that 3spd appearsthe same. OK, I'm changing my answer, it's from a '73 B100.
The shifter mounting bracket extends pretty far back. Wouldn't that be pretty awkward trying to shift gears with that in a van? It would be like reaching behind the seat to shift.
