For Peggy's birthday yesterday, I got the radiator issue fairly well figured out. The later radiator I had with the brackets that wouldn't allow it to work in this application turned out to be the correct size ... so I took a deep breath ... put a fresh battery on the sawzall ... and now the radiator fits. Mostly. The two upper brackets still need to come off in order for the grille cowling to sit down on the top of the radiator. The gap formed by the two brackets being there will prevent the radiator cap from fitting.

I was also able to do a rudimentary leak check on the radiator, too. So far, so good.
And it turns out that where Dean's Lurch has wire fasteners on the radiator supports, I had two sets of ... clips? that draw the parts together and hold them.