I just tossed the power steering on my car (69 mustang). I dunno about a 66, but from mid 67 through 70 (all the same), all you have to do is use a manual centerlink, pitman arm, and smaller bushing on the idler arm. If you don't feel like dropping everything, mustangs unlimited sells a piece that bolts on your existing centerlink and allows you to toss the power setup. This is all on mid 67-70 again, I'm not sure about 66, but I imagine the procedure is very close if not the same.
Metalhead, if you have a late 67 (there was a midyear change) and want to convert, I have everything necessary --- it's in great shape - just took it off my car a month ago. I'm about to sell the setup. I was going to put it on ebay, but if you want it, just email me and we can work something out.
nealkitchen@hotmail.com