Quick update:
I have now had my second part failure since the conversion over a year ago. There are only three non-Toyota parts used in the conversion. The coolant tube (which loosened), the electric fan, and the relay for that fan. Well, the other day I noticed that the radio shack relay (used because it was available) looked like it had gotten pretty hot at some point. Well, today on the drive home I parked in the driveway and the fan just kept making noise. Turns out the RS relay failed closed so the fan wouldn't shut off when I shut the truck off.
I just turned the thermostat up until it shut off via the control from that relay.
So, to date: that's two little problems with it. Both of them non-Toyota parts.
Let that be a lesson kids.
A whole 20 minutes to replace the relay (with another RS relay, because I don't have time to look into it more today), but next time I get some time off, it's time to redo that. In fact, I think I'll simply use that relay to power another relay which will actually turn on the fan (from a hot battery bus), because that way I can also add a completely separate power supply for the fan control, just in case the thermostat ever fails or something.
Dan