My ladder bars are just shy of being 6ft long, 3/4 heims front and rear, 1" DOM seamless tubing with .250 wall. Extended front radius arm mounts and mounted the front to them. I have a 107in. wheel-base.
Mark, There are WAY too many variables to go into in just a few sentences in a forum like this. I'd suggest that you purchase the book " Door Slammers: The Chassis Book" by Dave Morgan......It's ALL in there.I bought it before I started building chassis and I've never looked back......And yes, In part it has to do with instant center and yes, you'll have to accurately scale the car......
Rob