Try this before the next cold start: Turn on your headlights THEN turn the key to the "on" position to activate the glow plugs. When your "glow" light goes out, your headlights should get brighter. If not, the system is not working.
As for that pipe on the passenger side, it is as you suspected -- for crankcase ventilation. It's called a "draft tube". Some blowby gasses are normal, especially for a truck this old. The '84 and later engines had a hose to route these fumes back into the air intake. Isuzu even had a TSB and sold a retrofit kit to do this on the earlier ones. You can make your own for a couple of dollars with the instructions
HERE.
Before you worry about rings and valve guides, lets work through the simple stuff.
Manuals pop up now and then on eBay. I prefer the factory manual, but I've heard some of the others are good and some are weak.
Jack
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'83 Isuzu P'up Diesel LS - Original Owner
JoeIsuzu@IsuzuPup.comIsuzuPup.com