Ask our Australian friends who do track this MCA mod successfully. That's how I found out about these brackets. Some hard numbers are posted here:
http://www.ft86club.com/forums/showthread.php?t=112859
You can make of this what you will. The described improvements are real.
Modified LCA do not usually change the anti squat because they do not change the body mounting point.
They could do so if the hub end were made sufficiently high relative to the body end but they generally make these only to accommodate a lower spring mount.