Since I do at least have a pair of cylinder base gaskets among the bits and pieces that came with the bike I can get started putting her back together.
First thing is to clean the crankcase faces where the barrels mount so it’s a case of getting in there with a cloth and some Panel Wipe to give a clean metal surface.
The barrels themselves need the same treatment and then the greased gasket put in place on the barrel. I know the obvious is to put them onto the studs on the crankcase but that would have the base cover plates lying on top of the greased gasket and the plate acts as a support for the piston while fitting the barrel.
The bores were wiped clean and then given a wipe of oil, slipped over the pistons and slid home onto the case studs.
Access to the nuts on these studs is awkward, Velo supplied a special spanner for the job, which I don’t have of course so it’ll need to go onto the parts order so until that comes I’ll just spin the nuts on finger tight and await delivery.