I put in a specialty power windows wiper kit in my '40 chev pickup, and I have to say, that kit is one of the ONLY aftermarket kits left on my truck after 16 years.
http://www.specialtypowerwindows.com/main.php I have nothing but good things to say about them, and Classic Instruments.
The blades / arms and options there weren't great, but I feel the problem is mine hang from above the windshield and it's a high pressure area, so anything above 55mph and the blades / arms kept coming off. I wanted to keep it hung from above though as I like to open the windshield. They work well below that speed though. We did a 7000+ Mile trip last summer, so we just popped the wipers off and threw 'em behind the seat so we could do 75mph.
It is electric, and variable, even has the push in option to wash the windows. As far as the kit goes, simple and straight forward, If you do go with it, the key to a long life is to put very generous, wide bends in the drive tube.