[Phil]

Dean;
Fran is absolutely correct...the rolling radius of the tire is most important, so you may need to borrow a set of tires at proper inflation to get a really good measurement. I wouldn't fiddle too much with the lower arm....try to keep it as level as possible as changes here are going to affect your virtual swingarm and ultimately roll center.... also, if you set up the suspension correctly with the lower arm level you will find as you drop the arm camber will go positive since I am assuming that your upper arm is shorter. If the lower arm is level I would simply find a tire size the puts you where you want to be as far as ride height, and go from there, as this is probably the simplest solution.
Hope this all helps
Cheers
Phil