The first thing you need to do is see if your throttle cable bracket has the "button" or "post". If you have the "post" you will have to change the bracket in order to install cruise control. The post looks like a post and the button looks like a post with a cap on it. It is located on the side of the cable bracket.
I did mine by buying the pieces off Ebay. In fact, I have a new cruise control cable I made for it on Ebay for sale now that includes the "roll-off " switch connections. A friend of mine gave me a salvaged ultra overlay cable that I used instead since I am changing over to an Ultra Radio and getting rid of my side-car amp rear speaker set-up. The overlay harness has the wiring for both.
If you do have the button, send me a message and I will give you the part numbers and installation instructions you need to do the upgrade. There are a number of step motor part numbers that will work. I found it to be cheaper to piece together a kit that it was to buy one. Plus they are obsolete and hard to find.