My '77 D150 Custom with 318, PS, auto and AC (and spare wheel) normally weighed 4100-4200 lbs depending upon how much gas was in it. I used it to haul bulk feed, so it got weighed on certified scales quite often.
My folks '73 D100 Adventurer with 318 PS and auto (no AC) usually weighed around 3800 lbs. It too spent a lot of time hauling feed and running across the scales.
Some of the weight difference on the D150 came from the larger, heavier rear axle, also larger rear brake drums, the AC (a York hang on unit, lighter than the Chrysler V compressor). The D150 did not have the larger radiator found on the 4 wheel drives, nor did it have the little metal reinforcing plates at the bottom rear of the front fenders like the 4W.
For comparison, my '74 D300 with 318, NP435, rear dual wheels, 12' Knapheide flatbed and hoist weighs 6500-6600 depending upon how much gas is in it. With the metal grain sides on it will average 7200 lbs. It has a full load even before you put anything on the bed. After I added a home made tag axle, when hauling grain I would gross around 19,000 lbs. And the plate on the door shows the GVW as 10,000 lbs, meaning I was WAY overloaded. Still have the truck, has around 33,000 miles or so. Not many miles, but most of those miles were heavily loaded ones. The 318 just isn't really enough engine and when hauling grain loaded-empty round trip, I'd average about 6 mpg. I bet a 400 wouldn't do any worse and might do better. Don't row crop anymore, so no more of those severe overloads.