It may not be dealer fit, but dealer arranged. Back in that era GMH had a dealer fit setup so A/C could be added to plant stock vehicles to get a sale rather than order a new build. However like today it is cheaper to get a dealer to fit aftermarket rather than "genuine" eg canopy, hard lid etc. May explain why it is neater than most?

I learned to drive in a WB 3.3 M20 van and it went OK but with a 3.55 diff a bit low geared. I built a WB tonner in the late 80's as an everday driver too. I used a 202 as I had a good one out of my LX Torana, it was worked a little with YT head, nice cam, HEI dizzy and extractors with 2.25" system but stock Stromberg so probably had similar or a little more go than a stock blue 3.3. When I first built it I used an M20 and the 3.55 diff in it with 205/65/14 tyres. It was awful on the highway, so I stuck in a HZ 3.08:1 Salisbury. It was then horrible reversing, do I fitted a VK EFI trimatic. It was a great car on the highway after that and was also far easier reversing and carrying a load.
So that 6cyl one wouldn't be all that bad, probably has a 3.36:1 diff in it. Would be slightly heavier than my old tonner with alloy tray so may be slightly more sluggish. One of these would return similar economy to a 2tonne V6 SR5 Hilux, circa 20-25MPG. Better conversion would probably be an injected 5L and 4L60E.