As iWire has pointed out...
part of 250.104(B)
The equipment grounding conductor for the circuit that may energize the piping shall be permitted to serve as the bonding means.
In other words, the grounding (bonding conductor) used in the branch circuit thats feeding the furnace/ boiler is adequate of bonding the gas pipe. No, you do not need to run a seperate #6 cu wire from the panel to the furnace/ boiler. The gas pipe "feed" is not permitted to be used as part of the grouding electrode system.
Good luck!
