Your best bet is to cut all the rot out. Then get some heavy duty steel and reinforce that area. That is a critical point being it is the strut tower and where the K member bolts up. I saw a local fab shop just section som new metal. Look like 1/8" steel, and it looked great!
91 Mustang GT 4.6L 32V Cobra motor, T-45 trans, Bassani X-pipe, Flowmaster cat-back, 3.73's, Sub-frames, LCA's, SN95 dash, column, console swap. ABS, 5-lug, 4 wheel disc brakes, Cobra grill, spoiler, bumper.
04 Cobra--Whipple 2.3L,17psi, 595RWHP