If you are looking for advice, I'd advise, do not run a '67 or 68 Shelby with a rear anti-sway bar. Simply put they do not work.
You will induce severe understeer with the car with the rear bar. The bigger the bar, the worse it gets.
Maybe it is simply that the lowered front-a arms don't work with the rear bar? I'm not sure but I can tell you that I am 1,000% sure, it is a severe mistake to run one.
Don't ask me why they were included on '69 '70 Boss 302's. I don't have a clue.
Show me one R model that ran with them. I don't think so.