I would do it.. I have done it actually.. However, I have had problems with rubbing the inner valance and a hard turn since I did it. It seems that I need to shim out the upper A arm like they used to do for the earlier mustangs in order to get the alignment happy. Ive read on shelby forums of this same issue with actual racing shelby cars and the old fix for the issue was to cut the valance where the rub issues occured.
69 Grande' 351w, Performer Intake/Cam, Holley 670, Hooker Comp.Long Tubes, Flowmaster 2.5inch 40's, AOD, 9"w/3.70 Trac-Loc, Shelby Drop, GAT Mid-eye 4.5 leafs.