The table on a G0704 itself is 7.125 or so wide and the Y base is 13.25. If no overhang was allowed as is stock, the travel would be in the 6.125 range. 8 is possible with over travel occurring on both ends (possible due to the stepper mount and the column spacer. 12" would be impossible without an entirely different base. An inch or 2 of engagement of the gibs is not enough.
I think you must have got onto the Charter Oak/Industrial Hobbies site to see 12" Y travels.