The new lowers arrived today and they fit but there are a couple of points to note.
1. 20mm bolt through has same overall top to axle length but the point where they bolt to the spring & damper rods is about 20mm shorter, have had to put travel reducer spacer on to limit it to 100mm travel and the damper cartridge is slightly too long so it bottoms out with about 5mm still to go.
2. 20mm lowers are post mount so need a new adaptor to run 203mm rotor, fitted spare 160mm rotor for now.
They are noticably stiffer than the QR lowers, whether this is due to new bushes or not I don't know but they are loads better. It's a conversion well worth doing if you can pick the lowers up for £60 posted.