Hi guys, thanks for the comments. The strongback is internal and is resting on 4 vertical uprights. I have just slid the forms onto the SB in their approx location then fixed the first one no 16 half way up and centered across the top of the sb then sited each form against the first form in turn worked forward. Each form is square to the sb at its location but this leaves the last couple of forms fitted and in line with the previous form sitting tight on top of the sb. This leave a variation of approx 8mm height difference from the first form fitted to last, even though all the forms are lined up. The sb is a single peice 3, 3/4"x 1, 3/4" white wood beam.

Hi Patrick,
: My comments applied to an external strongback, not an internal one. I've not
: used an internal one, so perhaps someone else might be able to help you.
: You can search this site for previous posts on this matter. There have
: been some pretty refined techniques posted by some. You should read them
: and see. Otherwise gets Nick Schade's book. He explains it all in there as
: well.