I am in the process of finalizing an in tank pump on my 56 using a setup from Tanks Inc.
It's a lot of work but not has hard or scary as it looks.

The worst part was flattening the ridges and humps on the top of the tank. I had to heat and shrink the metal to create a flat spot for the flange. NOTE this tank has NOT had any fuel in it for over 15 Years, there were Zero fumes present, and no chance of combustion when using the torch to work the metal!!!!! If your tank has ever had fuel in it STAY AWAT FROM IT WITH A TORCH. I was cautioned that even flushing it with water would not be safe.

http://www.tanksinc.com/index.cfm/page/p...=prod/prd84.htm