Check the classifieds. There's a lot for sale there, and someone may have a set listed. Keep in mind that even if you find a seller with all of the parts, the ram, control valve and pump may need to be rebuilt, and the lines may need to be replaced with new...all that stuff is available. You could get a good idea on the price of rebuilt or new control valve, hydraulic lines, power steering ram and power steering pump on Rock Auto. Also keep in mind that the brackets for the pump will be different for a 6 cylinder car and a V-8, and conceivably different if your '66 has an A.I.R. smog pump on it still (California car).
also that steering rod from the box goes all the way to the nut that holds the steering wheel. so you will have some steering column work. good luck with your change over. my wife will not drive my 66 because i have manual steering. but she used to drive my 66 i had back in 70-72.
ive got the stock power steering off my 67 you would have to buy a pump,but i did put a new control valve in the cylinder a couple of years ago,worked fine when i took it off. you can email at [email protected] make me an offer