I just installed mine 3 months ago and there is nothing to it. I bought a new Granatelli unit off of ebay cheap and have been really happy with it. Keep in mind you will be letting air back into the brake lines so bleeding is nessesary afterward which proved to be difficult as you are going to be trapping air in the soloniod. If you have a Mity vac pump it makes bleeding them down easier. The rest is just straight forward electrical connections and you'll have a light to mount that illuminates when the system is turned on and switch which I hid under the shifter boot so its able to be held in my right hand. The instructions that come with them are good and you should allow yourself a full day and a couple of trips to the parts house for differing brake lines and adapters.
I bought the Summit brand line loc that looks like a Hurst Roll Control. I also bought the Summit universal installation kit. It included some tubing and several adapter fittings. Seemed a little pricey when I bought the installation kit ($25) but it had everything I needed for the conversion and so I spent zero time out running for parts.
You should also have a double flair kit on hand and some tubing bending tools to make life easier. I probably had an afternoon in mounting the line loc and wiring it up.
I think the hardest part was finding ample space on the apron since I also have an adjustable proportioning valve mounted there too.
The instructions were sufficient. You can view them on the Summit web site--check out both the instructions for the Summit brand and the Hurst brand (which is more detailed.) Just pull up the appropriate part # of the line loc and check out the description--there is a link to the PDF file.
Thats true about the installation kit, its a must have for this job. I recall now that my trips to the parts house were for fittings, lines and adapters for the Baer master cylinder and proportional valve.