You handling will diminish as you raise the rear using lifter shackles.
IMO the best way to add a rake is to spend a little money replacing your worn out springs. If you have already replaced/rebuild you suspension lowering the front is place to go for a slight rake look.
Judging from your profile pics here:
IMG_1838 Pictures - IMG_1838 Photos - Mustang Picture Gallery - AllFordMustangs.com you look to sit pretty level already, so I would simply pull the front coils and cut 1/4 coil of each and then reassemble, ride around the block, and check your height. If still not low enough take another 1/4 and repeat.