Good point BBBHC.
DLWilson, I'll be watching your build thread too as I'm looking to convert my neighbors cart. I was going to go 14S but the similicity of 12S is rather nice too. Remember, you don't want to go to 4.2vpc or down to 3.0vpc. Most people running lith will charge to 4.15vpc and go down to 3.15vpc. At 12S that'd be 49.8v down to 37.8v at the pack level.
When I switched to lithium I was amazed at the performance difference. It'll be interesting to see how well the DS performs with a 12S pack when you lighten the cart 400lbs (give or take).
Good luck!