when i ran a hacked mafs setup and later an s-afc/z32 mafs setup, i used 1.5 degree of retard for each psi, but some people suggest 1.75. i set mine to 16* and it worked great from 7 to 10 psi.

glad to see you got it running. had i done my car over it would definitely have been a t28 setup or gt28rs like yours. get it tuned good i wanna see waht that little sucker does at like 1 bar. (that will be the real fun)