Paul,
Adding a carbon-fiber shaft won't make it MORE bottom heavy; the "bottom-heaviness" is of course the result of a heavy coil (relatively speaking) at the end of a long "lever." The weight of the lever (shaft) in this case does not alter that equation much. However, adding some counterweight CAN address the "nose-heaviness" of the machine, which is why I offer a counterweighting system as one of the options, with my shaft system. While it seems counter-intiutive to "add weight" to a "light machine," in reality what many find, is that right amount of weight added, to offset the weight of the coil, can make for a MUCH more confortable machine, for many folks.
Steve