I put this here hoping for more exposure then it might get in the street rod section.
This is pretty long, please read the whole deal, I tried to answer all the questions up front.
The truck does not appear to be over heating, the whole deal only happened after the truck has gotten to operating temp and is shut off.

My 49 Dodge truck has a complete stock 96 Dakota chassis and 5.2 drive train on a stock (other then a wheel base shortening) Dakota 4x4 chassis. This was all factory stuff out of a 44K miles Dakota that rotted away.

The 49 sheet metal sits pretty low on the Dakota chassis, there is only about 4" of clearance above the factory air filter housing and the hood center. This created an issue with the factory radiator housing concerning the hood side clearances. I had to modify how the top of the radiator was held in place, but it worked with the stock Dakota aluminum & plastic radiator. Space under that hood is at a premium, I had to replace the original Dakota overflow bottle with a much smaller cheap plastic one. I don't believe that smaller overflow bottle was big enough. After a run and a stop, that overflow bottle would fill and spit out a bit of coolant, then when it cooled, it would suck it back into the radiator. every time it would spit out a bit more, until the bottle was empty. About once a month the coolant level in the radiator would be below the radiator cap level (very hard to check because the radiator cap was up under a section of the hood that does not open.

The OEM aluminum /plastic radiator started leaking at the tank/core seem. I replaced it with an aluminum crossflow with an electric cooling fan that fit in the hole much better. Its a slightly smaller core then the OEM, but it is a 4 core rather then the 2 core OEM. This radiator is suppose to cool 450HP, that 5.2 isn't anywhere near that HP. The top of this radiator is several inches below the highest point to the cooling system (where the upper radiator hose goes over top of the AC compressor, the AC does not yet function). I've added an in hose radiator cap into the highest point in the upper hose as an attempt to keep the cooling system full and I relocated the over flow hoses to the top cap. Using the same overflow small tank in the same location about even with the top of the radiator, I experienced the same coolant loss as I did with the OEM radiator, but at least I could top off the radiator easier. I was adding about a 1/2 quart a month, it was always over flowing and dumping it on the ground after the truck was shut off. The cooing fan functions, but rarely runs, When it does run, it brings the coolant temp down quickly and only runs a few seconds and shuts off. The factory gauge does not show it running hot. .

I've replaced that overflow tank with a better tank (but not much larger) in a position that is even with the in hose radiator cap, that new tank is only a 1 liter tank. No larger tanks will fit under my hood, but there is enough space I can add anther 1 liter tank along side of the one I have. If I add a 2nd tank, and plumb both together, do you think I will solve my over flow problem?
Pictures, 1 & 2 the OEM vertical flow on the bottom and the new aluminum radiator on top, see the difference, the OEM is a 2 core, the Aluminum is a 4 core.
pic 3, Current recovery tank with the hose mounted in line cap, and how it looks under that hood. Space is a premium.