I tidied up the wiring as much as I could, and tested all the lights. Everything works, except the extra brake lights that I wired in ages ago where the factory fog lights would go. I think that's most likely to be my soldering in the light units, as the main brake lights work just fine. I buttoned everything up, tested it all again and called it "good" :o)
I've bought new wiper blades, so I installed those while it was relatively easy to do. I've kept the fittings to see if they'll work on Gwen's Jeep.