Intellitronics dash for 70-76 A body!

The company installation sheet makes it look like the speedo works only with an electronic unit, not the old tried and true cable. What's involved in changing all that? For example, to work with the 200-4R in my 73 Sport.
I have asked them a question about that. If you look at the instructions of the speedometer sender, it look like it attaches to the cable outlet from the transmission. So it should work.