I would be VERY cautious about moving weight back. Looks to me like you're close to ideal. The goal is to leave so little weight on the fronts that the effect on rear loading is negligible while, at the same time, avoiding a wheelstand.
Page 28 of the following can help you in adjusting a 4link. See Page 9 if you're interested in canceling driveshaft torque effects:
http://home.earthlink.net/~whshope