Ok, got it done. Hours ago. Everything went fine, albeit slowly.
Actually, I still have a little drip going. Those old seat valves suck; they close once every other decade and then they leak. So I’ll probably snip the inlet pipe a bit shorter and stick on a nice 1/4 turn ball valve. One with one end a compression fitting, the other end a standard garden hose thread would be perfect.
Drip seems to have stopped this morning. Now on to my next holiday project: fixing the toilet, which has started to leak. Probably just needs a new wax ring, but that means another 12 mile drive to the hardware store. And she probably wants me to take her to the mall today!