The bung for the coolant temperature sensor worked perfectly and he successfully relocated the upper inlet to the right (passenger) side of the tank to better align with the later model 4.0 water pump outlet. No leaks, not even a drip from either of those locations, but...
We had always noticed the filler neck was bent, downward, as if something was under the hood - on the radiator - when the hood slammed down at some point in it's past. What we hadn't noticed until we were working on it was that the upper tank was also bent, swayed, down in the center to a now-noticeable degree. Connecting the radiator the engine and filling everything worked great. Ran the engine for about 15-20 minutes and then put the cap on to pressurize the system. Niagra Falls. Not from our solder joints, but from the capillary tubes.
Out came the radiator. Solder the leaks. Pressure test it with a bicycle inner tube between the inlet and outlet and some soapy water. Looks good, put it back in, heat it back up with the 7lb cap back on, half-an-hour later, leaks.
Drain, desolder the frame from the upper tank to gain access to the new leaks (plural), repair, test, reinstall, run, you guessed it. More of the same a little later. Bench test with air is good, but it doesn't respond well to a combination of heat, fluid, and time.
I originally thought the previous owners cap was too high pressure since the tubes pop before the spring lifts, but from what I've read here, 7lbs seems ok.
Further inspection reveals many of the tubes are bowed or bent and are brittle from whatever downward stress they underwent. I'm not about to send him down the road with this one even if I could get it to hold for a time. My question to those reading is this:
From what I've seen in the aftermarket for 6cyl radiators, some already have the upper inlet on the right side. Are wagon and truck radiators different? We can go about cutting-up a brand new one, but if we don't have to that would be ok with me.
With our cooling system efforts at a momentary halt, we pulled the rear springs and took them over to the local spring shop. I should have a quote by phone in a day or two regarding new spring packs and re-bushed shackles.