It’s a set of S&S couplers – they’re mounted in a teeny donor frame right now, but I have a torch and I’m not afraid to use it – for slightly more than the minimum framebuilder price estimate the S&S people provide on their website. They look like they might be 25 & 28mm, which would be spectacularly perfect, but if they’re oversized I can just upsize and downwall the frame selection.
Plus it will give me a donor frame that I can experiment with doing a nondestructive front triangle retubing.
(The boss battle will be to make a S&S coupled tadpole for post GCS and post kidney donation riding, but that’s not going to happen until the zap! bike is glued together.)