: I don't know that particular build's idiosycracies, but the important
: elements to be 'square' or aligned - are the forms - not the strongback
: (external or internal).
: So is there any simple way to align the form in question independently of the
: strongback? Like a couple of angled shims at screw or bolt locations? -
: that method is adjustable and possibly could account for any strongback
: malformation.

this is a pic from vaclav's one ocean site where he shows that the strongback cut is not necessary to be exact. This then allows one to fine tune the location with small wedges as is plainly shown.

So, overcut and then wedge back to the location you want, then tighten the bolt/screws.