@daniel.watters - Actually, as my wife and I feel the approaching color selection deadline, we've been looking over the options quite a bit lately, and River is definitely a strong possibility. I don't know if it was really ever used on a '64 FJ40, but obviously some Toyota model(s) must have been painted in River.
Progress today. Spent most of the day continuing to strip the tub, with an occasional side distraction.
Distraction #1 - disassemble inside mirror so that I can paint it and replace the glass.
Pleasant surprise, not as bad as I feared under the tank. Or at least, so far. We'll see what's left after blasting.
Beyond that, got pretty much everything stripped off, bagged and labeled. Biggest find today is that the tub is warped. Passenger A pillar is not vertical, off by 2° from the driver side. Over 5/8" (15mm) difference from windshield base to B-pillar from side to side. This is why I couldn't get either the passenger fender nor the right door to fit well. Pleased I found this now, it shouldn't be hard to correct, and will make fitting the parts back on much easier.