I think I have nirvana for my Hammond B3 sounds. I have been using the Roland VK8M Drawbar module for a few years. I use this in combination with a wide variety of midi capable keyboards; from the Tyros 2 to the Korg Triton Extreme. The sounds of the Roland are amazingly realistic and perfect for live gigging. The module weighs very little.
I can't see just bringing a Hammond on a gig unless I'm playing Blues all night, so I need a variety of sounds for different songs. That makes this module very handy.
Tyros 2, Yamaha P-250, Korg Triton Extreme 76, Roland VK8-M, DW Collectors Series Drums, Roland SPD-S.