Update: I waited some many weeks before even looking at it after the last post.
So, I got a new radiator cap and put it on. The vehicle started right up; after running 5-10 minutes, I tried to restart it, with no success, BUT, there was no leaking from the radiator cap, so, I knew things were looking up. I mentioned it to somebody at work, and he said that a low radiator on a hot Durango engine would trigger sensors that would keep it from starting. I went into the “pipe/tube” part of the system and put new coolant into there, since the “radiator” looked full.
I checked oil and it wasn’t foamy, BUT, I then decided to add oil. I pulled the oil cap off and found that the funnel part of the place to pour oil into had a milkshake foam all around the wall! Talk about effing weird, with much sorrow! I wiped the wall out, as best I could. I then, rather than break my heart further, just decided to leave the whole thing for a few more weeks, since this was my backup vehicle.
At any rate I decided that if there was a blown head gasket I didn’t give a shit, since I was tired of messing with vehicle technology newer than 1969, and wasn’t going to pay the price of a headgasket repair for a 15 year old truck, and said to myself that I would just drive it till it drops.
I started it up yesterday, waited for it to get warm, and, then, restarted it. It worked like a charm. Took it driving around town, and, no problems. Rechecked the oil, and there was still no foam down there, and rechecked the funnel part and the remaining foam had pretty much dried. I also checked for the tapping sound, and, the offensive one that I referenced earlier seems to have disappeared, but, since it’s an old truck with plenty of taps in it, I couldn’t be sure. But, I don’t care!
tl;dr, replaced the radiator cap, added coolant, and this rascal runs great.
Thanks for all of your help, guys!