The shock towers on my '68 Barracuda were only attached to the inner fenderwells with a few spot welds at the very top. Several of them were starting to tear through the sheet metal of the inner fender.
I welded them solidly to the inner fenderwell, and then installed my USCT bracing. I have the old style ones with round tubing.
I welded in the front frame rail brace in too. I fab'd up a Monte Carlo brace, and that is when the last remnants of cowl shake disappeared.