Hi Erik,
Dont forget about the focuser also being on centre to secondary, not sure if your RC's focuser can be centered or if you can put a shim in.
Check my post there is a RC being centered with a laser (focuser end) and you can mark the centre on the secondary cap (cover) on secondary housing.
See link.
http://www.iceinspace.com.au/forum/s...d.php?t=103784
Den