I have the FSA bb392 tandem cranksets coming from Precision Tandems. The supply of those seems to be drying up. The “modular” nature of the crankset would seem to indicate that I should be able to dial in the stoker chain line for Shimano 12s. The spindle on my current captain’s FSA SL-K crankset is badly scored and creaking like crazy, so it needed replacing no matter what I ended up doing with the stoker crankset.

For the external Di2, I have the wire heat-shrunk to the rear brake housing so the only visible wires are at the derailleurs and the external battery.