67 sway bar in a 66?

To my knowledge, that doesn't work.
That's why there is a factory sway bar for the 65, 66, A body cars, and a bar for the 67-72 cars.
Sway bar mounting bracketry to the crossmember is quite different between 65-66 and 67-72.

My .02 cents is if your looking for a bar for a 66 car, advertise for one in the for sale section.
They do come up for sale from time to time, but admittedly, they are hard to come by.