I started by getting a rebuilt '67 steering box with the short shaft and 1 1/8" sector shaft, a 67/70 pitman arm and a collapsible steering column from a '68 Mustang. In order to remove the original '66 box, you will need to remove the column housing first. Next, if you have a 4 speed tranny,  remove the clutch equalizer bar. The shaft will need to be cut off close to the box using a cutoff wheel (I used a dremel tool with a fiberglass cutoff wheel). Remove the steering linkage from the pitman arm, you don't have to remove the pitman arm, unbolt the box from the frame and take it out from the top. If there is no engine in the car then the box and shaft can be taken out without cutting it. Mount the new box in place temporarily.

 Lay the new shaft beside the old one and adjust the shaft so it is the same length as the old one. The splines where the steering wheel adapter goes should be even with each other or the steering wheel will end up in a different place. Install the shaft, with rag joint attached, onto the box and slide the column housing down over the shaft until the upper bearing is seated against the snap ring. Mark where the dash clamp holds the column to the dash then remove the column. Cut a 1" long slot centered approximately 15" from the lower end of the column to allow the tab inside the U-shaped dash bracket to fit in and allow for some adjustment. Put the column back in place and against the upper bearing and bolt up and tighten the dash bracket.

 You will need a mount of some kind to hold the firewall end of the column in place. I opted to make my own by modifying a mount from a mid '70's Ford pickup truck. I had to cut it down until it fit in the position of the original metal sealing ring.  With the column in place and the new mount  slid against the firewall, I marked 2 of the 3 holes that held the old seal ring in place. I did this by placing a drop of  black paint on the end of a piece of wire and (from the engine side of the firewall) stuck the wire through the 2 top holes to mark there location on the mount. After removing the column and the mount, I used the old seal ring to mark the 3rd hole by placing it on the mount and lining it up with the 2 holes that were just marked with the paint.  I then drilled the holes, making them a little larger than the screws in order to allow for some adjustment so I could center the column around the steering shaft. After cleaning and painting everything, I was ready to install the column and begin to hook up the wiring.

The wiring was pretty simple, since the color coding of the '68 is the same as the '66 column except for the emergency flashers. My '66 didn't have the emergency flashers originally so I had to add a few wires and another flasher to make it work. I removed the '68 wiring coupler and connected the wires to the '66 coupler wiring and soldered the connections and used heat shrink tubing over the joints.