I'm also in the process of designing a 4-link rear and have found a few resources that have really helped.
This thread from
Pirate has tons of info.
After getting a good understanding of the forces involved I started modeling in CAD. I have drawn a complete plan and elevation view of the frame, axles and tires and use that to play with the links.
I believe its a CalPoly student that wrote this
link calculator. Awesome program. You enter in the rig specs, X,Y, and Z axis for each end of the links and it plots out your Roll Center, Roll Axis, Instant Center and calculates your anti-squat %.
The hard part (for me at least) is that there are few if any good rules to follow. Everyone seems to have a different opinion as to what values make for a good 4-link.
These are my goals -
AS% between 75 and 100
Instant center in front of front tire
High roll center ~24"
Roll Axis slightly negative (sloping to the front)
Its going to be awhile before I start making links
HTH
Matt