hello all, i've a 79 W150 w a 360 2bbl... i was headed out hunting one morning last week and lost hot air from my heater... 2-3 minutes later the headlights/instrument cluster got markedly brighter for 20-30 seconds then the engine started sputtering as though it were running out of gas, i switched to my auxiliary tank but it made no difference and in a couple more seconds it started sounding like it was missing or dieseling (term i've heard used for when your carbed motor keeps running for a few seconds after you shut it down on a hot day). at that point i pulled over and when the wind caught up with me there was smoke everywhere. further inspection revealed that it was all from coolant burning off as it was all over the underside and even spattered on the tailgate. all hoses and lines seem to be intact. when i add water to the radiator there comes a point where the water begins pouring out of the back side of the motor about as fast as i can add it to the radiator. seems like head gasket or cracked block or head are possibilities but one would expect these things to issue a slower leak of fluid than what i see with zero pressure on the system. this leads me to think it could be a freeze plug failure. i've been unable to get a direct visual on the leak at this point because of its location. oil seems unaffected in terms of volume and consistency/color. i did crank it up for a short time before adding water and this produced a white colored smoke from the passenger side pipe, but not the driver's (true dual exhaust, no cat, glass packs). there is no smoke from the pipe since adding water to the system. i did observe what appeared to be fresh moisture on top of the tranny bell housing, seeming to suggest the leak is fairly high up on the motor. i'm unsure of freeze plug locations around the back side.
SO.... am i pointed in a solid direction to consider freeze plug failure? regardless of the issue, because of the leak location, i'm pretty certain i'll wind up having to pull the engine to perform repair, i'm just trying to wrap my head around the situation before i start digging in too deep.
this is not a daily driver... just a family heirloom. i have an event in june, for which i always drive this truck, but other than that, no demand to move quickly. i appreciate any help, theories, suggestions, or other sage wisdom any of you guys or gals can impart. have a great day!

 

it might be easy to just pull the engine. but get brass soft plugs. and dont forget the ones in the back of the block. in the back off the block the hole in the middle is a plug to cover the end of the camshaft dont remove it.

 

might be easier to drop transmission I had to do the same once the freeze plug rusted out in the back of the block I was told to get the longest bolts you can find for the bellhousing and install them and slide the tranny back as far as it will go on the bolts and tie up the tailshaft on the body or frame makes it a lot easier but if yours is like mine the crossmember will be hard to get the bolts out

 

I'd start with a compression test, especially for cylinder 8. High up and white smoke out one side leads me to head gasket failure. A leakdown test would be best.
Do you have water in oil?
Cracked block due to freeze happens in the valley area under the intake manifold in my experience. Block side expansion plugs may be able to be replaced without pulling the engine.