This morning I installed the shifter cable for rear derailleur and I'm happy to say the shifters from the donor bike work perfectly, even though kinda outdated. I also installed a front brake, although it's not very good and I'll likely buy a new one soon.
A couple of other details got attention today. First I took my calipers with me to Goodwill in hopes of finding another donor bike to give me a proper stem to fit these handlebars and the fork. The shims I made for the original stem were slipping. I found this Princess bike with the right stem and it only cost me $4.99. Checking compatibility in this photo:
And here it is installed:
This stem is much better. Glad to have this problem solved. My daughter wants to ride the princess bike now so we'll have to find another stem for it. :)
I also noticed the chain was rubbing the rear shifter cable a bit, so I solved this by adding a washer to the idler to shove it out about 2mm. This did the trick.
I've been riding the bike all over town today and it's excellent. The guys at Recycled Cycles were impressed, too. I do need to practice tight turns, though. They're hard on this long wheelbase. Last thing to do is install front derailleur. No urgency to this though.