1986 GMC Astro rebuild...questions

Grills: The small ones Semi spoke of were very small, pre 79 or 78. Air flow was not all that bad as they pulled a lot of air in through the holes in the bumper. The radiators were also that tall. I saw one with a factory V12. Late model tall grills pulled no air in the top section. It was just a flip lid with a latch, access to check coolant and oil. Yours must be an economy version like the dash.
Dash Valves? One likely is for the odd air bag on the front axle but I am not familiar with that suspension.
The other one I can only imagine could be for an air shift 2 speed differential, locking axle ( a picture of the left front of the axle housing can answer that ) or a low range in the transmission. Some of the older rangers had a deep reduction switch on the dash. I drove a 4000 White a couple of times with a range valve on the gear stick. The air valve was only used on the top or bottom one or two gears. Steel plate said it was a Spicer 6+1 but I have no idea what was at the bottom of the stick.
Can someone shoot this guy a Bendix air dryer/governor diagram? Or just google that.

 

Didnt think the astro cab was big enough to fit a v12 under it. Only seen them in double bunk petes and kws.

 

The engine wasn't always confined under the cab. I remember the Dodge L series, day cab, with a slant six, the engine would stick out from under the cab.
There was the little 4 cylinder General Motor Diesels that were red lined at 2500 rpm's. Low carbon build up! Then there was the unmistakable sound of the "Buzzin' Dozen". State patrol used to love the old Detroit's be cause if they lost one in a chase, they could always track them down by following the oil trail.

 

I thought the same but it was marked some how. Thank it had a little V12 emblems like I remember V6 emblems on smaller gas trucks years ago. I had to look and it appeared factory. They just moved back the transmission and shorted the driveshaft.

 

I've still got a 12v92 in my barn. Every year or so i pour oil in the cylinders and turn it over with a breaker bar. One of these days I'm gonna have to figure out what to do with it. Maybe slap it in a sled truck.

And fyi, no oil leaks when i ran it. But would puke it out the blowby tube when i idled.

 

Did you actually look at the engine and visually confirm it was a 12v?

 

Surprisingly, they did use them in COE. The GM "twin six" gas engine option. They had 4 valve covers and exhaust manifolds so it looked like two sixes welded together.

I'd like to see behind the cab of one.