Getting ready to convert my 70, these are the notes I have:

For a conversion on a 1970-1971 E-Body or a 1971 B-Body from a 2-spd to a 3 or variable spd motor, you will have to replace the wiper motor crank with part #2822289, also the link from the motor to the drivers side pivot with part #2822293 (1970) or 3431102 (1971). Note the part #s are stamped in these parts. The 1970 link will work on the 1971 and vice versa.

Parts List:
Motor: 3431077
Crank: 2822289
Switch: 2770380
Link: 2822293 or 3431102 (These interchangeable)

Although different PNs the E body and 71 B body links are supposed to interchange.
I have the 3431102, so I'll find out.