[Freddo]

A couple of things to consider on the radiator: I'm not sure how things work now, but when this truck (and radiator) was built, most of the radiator shops used a 60-40 type solder and they cleaned the surface to be soldered with 'soldering salts' or some type of cleaner for this purpose. Then they would apply a tinning compound which helps the solder stick to the tank and the outlet. The 'proper' repair is likely going to be to melt the solder around the outlet, remove it completely, clean it, tin it, and completely resolder it. You can try to patch the leaky spot and you might get it to hold...Maybe even for quite a while, but usually the hole just expands to another area on the outlet.
How is the radiator doing keeping the truck cool? If it's the original, it's pretty old. One benefit to taking it to a radiator shop is that many of them (Not all) have a machine called a 'flow tester' which will tell you how many gallons per minute of coolant your radiator is flowing. For example, if the radiator was capable of flowing 20 gallons per minute when new, and is flowing 14 or 15 gallons per minute, it's probably not in too bad shape. On the other hand, if it is flowing 8 gallons per minute, it's plugged up pretty bad and not what you would want to use to do some heavy working on a hot day.
Many radiator shops will flow test them for you at no charge if you bring them in.
Things have changed quite a bit in the radiator business since the 1970's when my dad owned a radiator shop. (Plastic tanks etc), but maybe worth calling the shop to see if they can and will flow test it for no charge if you bring it in. A good flowing radiator that the radiator guy says is in pretty good shape might be worth spending a few bucks on to do a long lasting repair. If it's 50% plugged, drive it around, watch the temp gauge and try your hand at soldering the leak. Hope this helps.