First, the front bottom bracket. The shell is so thin that each set screw only has a few threads available to engage.
A friend-with-a-welder beefed up this area by welding a pair of M6-threaded nuts over the existing holes
I can torque these bolts without worrying about damaging the threads.
Second, after I took the bike apart, I realized the two sync chain wheels weren't in a good chainline. Also, the stoker crankset wasn't setup for the best chainline, either. So, I spent some time mathing out a solution: 123mm bottom brackets front and rear, with the drive chainring mounted to the inside of the crank spider.
Last, I wanted to replace the drive chainring because it wasn't "round"; the mounting holes were not concentric, which means there was a high spot and a low spot in the chain tension as the cranks are rotated. Which is all the time.
Here we go:
This new frame color is Antique Bronze. It's metallic, so it really lights up in the sun.