The 700R4 all the way. GM kept improving on the transmission through the years. Most of the internal parts from the 4L70, 4L65, and4L60 are interchangable. I recommend a mild shift kit in one. I put a Transgo NOYOYO kit in an 85 K10 truck, it made all the difference in the world.

These guys are 700R4 experts: http://www.transmissioncenter.com/

1954 3600 Chevy Truck
"The Fake Truck"
In the Stovebolt Gallery
More pix on Photobucket