The agreed consensus is that Vans method of drilling the z brackets is not the best. I printed off Dan Checkoway's log from 5 June 2002 and have used that as my supplement to the build manual, Richard Horan also has a very detailed section on this which I also used to study the method.
Just to add to Dan's instructions I though I would clarify the bolt hole offset with some photos.
Since this log both the previous websites have been taken off air but I leave the links in the hope that they may return one day. In the mean time Jason Beaver has covered this subject very well.
The purpose of the bolt hole offset (1/16") towards the bracket web, EXCEPT the inboard one, is to allow you to get your pop rivet tool to the forward flange of the bracket when you rivet the bracket to the baffle/tank rib. To assist even more Simon grinded down the top of my pop rivet tool as I don't want any problems when I rivet them {Post note - worked like a dream}
