If you leave them loose-ish till you mount the suspension brackets then, you can just put them to suit saving you have to pack them out.
Im not aware the mounting jigs are out in the book, although most people make timber jigs which are easier I think.
If you check out Andy's blog theres some good info and the plans for a timber jig
http://bamaroadster.blogspot.co.uk/2...design_15.html
Cheers Will