JonC, I use Kent Jaquith to rebuild my vacuum wipers. He's a long time V-8er and has been in the wiper repair business for years. I had him rebuild the wiper for my 41 pickup and my 40 coupe. Both work excellent. Kent can be reached at ph#541-923-4319 or his cell # 541-350-7426. Kent lives on Oregon.
As an alternative look at the electric wiper that is put out by Pacific Western Design in Washington.
www.pacificwesterndesign.com. They have the Mighty Wiper which might work for you.
Just for info the pot metal housings for the pickup wipers were prone to pitting inside. Some can be saved and some cannot be repaired.