Greetings all, the tail is strings through the the unit not through the guitar, working out the location of the tail i am going to be masking tape to guitar top, clamp into place as suggested, use my steel straight edge in place of the strings to line up the unit to get it centered and set for length for intonation, drive in a couple of screws then use the strings to double check, once i'm happy i will then draw the out line of the plate then add the rebates where needed.
Yes i did set the neck before doing any other work, to do this i clamped body and neck and then used a straight edge steel to check on line and rake also making sure the truss rod was backed off.