I've had this one recorded for a long time. All things point to it being a Sandman. Metallic paint is supposed to be Sandman only on a HQ Belmont. M22 is standard fitment when 4spd optioned on a HQ 801 or 802 commercial. They weren't even called an M22 prior to 1974, just a wide ratio M20. Same deal as an XU-1 4spd, these are a close ratio M20. I think the HQ Sandman sales brochure is incorrect in this area where it says the 173 and 202 come with the 3.05:1 1st gear M20 where all other evidence including vehilces found to date shows M22 (3.74:1 1st gear).
If the body is half decent $6k is good buying in my eyes. To me as a restorer it is a better van than a 308 4spd as you can restore it to its former glory colour and trim wise (gunmetal with black is a nice combo) but run whatever driveline you desire like 350 and TH400, 308 5spd, 304EFI and 4L60 or whatever else you like and not greatly affect its resale value as it was only a 202, M22, 3.55:1 diff and most likely 4 wheel drums. Keep the original driveline on a pallet!