Those hood cutouts are not on any of my M880 series trucks.
However, my 1978 Air Force contract W400 has those cutouts. 78 was the last year for the birdbath hoods.
As was mentioned above, it ain't nothing but a 76/77 W200 non egr due to the 8,000# gvw
the factory payload of a W200 is 2500lbs...