I did this 2 or 3 years ago, my car is a 1970 also. The most important thing I found was getting the correct parts.
Wiper motor - 3431077
Motor crank - 2822289
Link(from crank) - 2822293
Var. spd swc - 2770380
The rest was just bolt on and plug in. I didn't change anything in the connector to the new switch as far as I recall. The ballast resistor is only for 2 speed applications.
Sorry, just dawned on me that you're converting to a 3 speed. Since the switches are a different size it looks like there will be the need for some connector modification.