Thanks Spile.
As far as I can tell, the earlier steps seem fine already and the mirrors appear circular and concentric.
Beyond that, I'm now confused. Your guide says the cross hairs and primary centre should be aligned by adjusting secondary tilt, with primary adjustment only used to align primary centre and reflected Cheshire centre. The astrobaby guide (which I gather is well regarded) says only use Cheshire for primary adjustment, which will align all 3: "It may be that that the pattern is offset and will show the cross hairs as being adrift from the central circle created by the Primary Mirrors centre spot and that the centre spots are adrift. If this is so then you will need to adjust the primary mirror". Idid think that aligning all 3 with one adjustment sounded challenging.
Which guide is right? Or am I misunderstanding one of them?