Some mild progress, and then a rabbit hole...
Aside from apparently being the wrong ones, at least one of my fusible links was also on its very last legs. One day I'll probably switch to a fused distribution block, but until then I came up with this alternative. The toughest part was sourcing the quick disconnects, since the fuses and the car wiring are both 5/16" instead of the common 1/4".
The fan always seemed to spin a lot (not siezed, but a lot of wind noise), so I pulled out and cleaned up the fan clutch as well. There's a hobby store down the street that seels silicone oil for RC cars, so I got a bottle of the 6000 weight stuff and kind of guesstimated on the amount to use. About half of the 60ml bottle seemed like a good starting point. So far so good.
Having found that thermostat housing last weekend, and not having done a flush or other work on the cooling system since owneing the car, it seemed like as good a time as any to give it a bit of attention. The coolant came out green, but I still flushed out a lot of brown gunk, and the overflow tank was pretty sad, but so far so good.
Then things went a bit sideways...I got all the sensors out of the new housing except for the temp gauge, which is quite-nicely stuck. I hope I can drill it out. The old housing is in rough shape, and other than the coolant temp sensor, there may not much much I can salvage out of it. And then I pulled off the radiator hose and saw what the water pump inlet looks like, so I guess I have to source one of those, too.