Thanks blokes.
Max, the crankshaft was fabricated, as per Elmer's instructions (well, almost as per). It was one of the easier crankshafts to do, with that big 'flywheel' section in the middle.
Nick, the 'pivoty' bit is actually fixed in position, it is really only there to carry the tensioning screws that bear on the balls/springs that hold the cylinders up against the port faces. There are a number of ways of doing this, but that is the Gospel according to Elmer, so I went with it.
Looks pretty grubby there, covered in oily fingerprints - it was straight from a running in session on the lathe