Double stem
I couldn't find a 31.8 x 31.8 "double stem" (really two clamps) comercially available so I made these myself with the help of a local machine shop (they bored the 31.8 diameter holes - I did the rest). Since then I've noticed that Litepro now make some which are intended for Birdy although I estimate the centre distance to be about 70mm between the bores:
https://liteprobicycle.com/en-gb/pro...-birdy-bicycle
Saddle and sliding saddle clamp both in fully rearward position.
Apologies for the blurred pic.
My ultralight kit came with fully built up wheels. Rear hub is from Hubsmith and included the XD driver for the e13 cassette.
My Tubolito patch kit is glue type. It was the 30min curing time that was the killer for me.