I looked over the rear seatpost and found that it is actually in good shape. There was a bent up aluminum shim around the top part and that made it look a little jacked up. But I removed that and cleaned it up, tightened the seat clamp and ta da! I also got a better look at the weird clamp mechanism dangling from the rear seatpost, and it appears to be more or less intact, but missing a semicircular wedge piece that would form the bottom half of the clamp. The seatpost itself has some spring to it for shock absorption, and that all seems to be in working order.
I also scraped off the jockey wheels and lubed the derailleurs and the chains. I checked the chains for wear, but both are totally fine. The brake pads also seem to be original and very much not worn. I need to look into it, but there’s a small (adjustment?) screw on each brake pad that I imagine might be used to adjust the angle for toe in.
I took the rear seat post to the Gear Hub and dug around in a box of parts, and I did find a wedge that should work. It was a millimeter or so too wide to fit between the two screws on the clamp, but luckily I recently purchased a bench grinder, so when I got home I put on my safety goggles and my work gloves and my denim jacket (and I finished attaching the protective shields to the wheel) and I carefully ground it down on both sides until it fit. Then I went ahead and switched out the front saddle onto that clamp and put the whole thing on the bike.
I had an old Avocet laying around, so I put that on the front of the bike just to give me something to ride on for now. If I ever plan to take a long ride with someone I’ll probably switch it out for one of my regular saddles. And it’s an old fashioned clamp mechanism on the front seat, so I will have to get one that adjusts easier to replace the front one. But on the bright side, I should be able to turn that old clamp upside down and put a saddle on there, then keep that one handy for rides with Ezra. By reversing the clamp and flipping it the saddle height in the rear becomes and inch or so lower, and that should just about allow Ezra to reach the pedals and ride comfortably as a stoker. Then when I want to ride with an adult I can just switch out the whole rear seat post. Quick and easy!
I did a little bit of test riding today since the sun decided to come out. The rear derailleur works well, but I had trouble shifting the chain onto the largest cog. The jockey wheel was bumping up against it. It’s possible that the chain will need to be on the smallest chainring in order to get there, but the front derailleur also needed some adjusting and I ran out of time. Boo! The shifting was smooth, though, otherwise. The bike will need a thorough cleaning, then I’ll re-lube everything and give it another go. And I still need to adjust the position of the two sets of crank arms so they are in synch. Either way I’m still really happy with the purchase. I feel like I found pretty much what I was looking for, and it doesn’t require any major work to get it rideable. Now I just need some good weather, some spare time, and a friend with the same.