Kevin, I had to laugh at myself when I read your suggestion of laying the radiator face down and using a couple of feet of radiator hose to get water into it to test it! (I could have saved myself some $$ if I had been smart enough to come up with your plan!
I am attaching a couple photos of a soldering iron I have on hand that has a bit of a larger tip on it. Is it as large as you think I should have, or are you suggesting one of those irons that are about 1" wide? (Serious question!)
Nick 1940 KC Model 1/2 Ton Pickup Project (with '37-'39 Bed and what we think is a '42-'46 Frame) Taos, New Mexico