Oh, while I was doing the test drive, the rear carburetor needle/seat/float failed again. This, after I was able to drive the car many times, and trouble free for about 100 miles. I was about a quarter mile from the house, and the engine started to fail to idle. I wasn't sure what the problem was, so I limped it home. When I opened the hood, I smelled gas, and saw that fuel was all over the place and dripping onto the header.
Awesome.
I decided to take a thin wire and reach down the float vent tube... to tap the float, which in theory, would unstick it. I tapped the float down and it bobbed back up again. I did this several times, and could hear the float contact the needle when it would bounce back up. Bounce, bounce, bounce, followed by tap, tap, tap. I turned the ignition key and several geysers of fuel came out the float vent.
Awesome.
I stopped there. I think I will replace the needle and seat next. There must be something wrong with it.