I just finished this repair last month. I did cut the upper cowl completely off. I have alot of rust around my vents and about 2" away from vent in spots so one of the repair kits would not work. I cut the vents out and fabed flat metal to slop to the corner so water would flow and welded in. Wire brushed lower cowl and put KBS coating (same as POR-15) on 2 coats, the done the same on bottom side of upper cowl. Welded everything back together.
I will be using vintage air on my car
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1968 Mustang installing AJE K-member strut with 95 spindle setup also full running works from a 1995 mustang GT, EFI 5.0, T5 built to handle 600hp, and 8.8 rearend.