G'day Peter & all
I think I'm only a couple of moves in front of you
I downloaded this :
http://www.spot-on-sundials.com/calculator.html & set up a plumb bob suspended off a 10 foot ladder and laid a long straight piece of timber on it's shadow as Jimmy did at Solar noon(11.52 am for me)
I then transfered the line to a mark on each opposing wall where upon I use a cheap laser to line up the tripod
,I now get the scp every time I set up
Good luck with it all
Bryan