The reason they are short is the valve covers and space available. The valk cobra driver boards are actually smaller passenger boards made to fit the front mounts.
The largest bolt-up driver boards I know of for valk are the MC Enterprises boards, but they always/often come in a kit with their own heel/toe shifter, and are expensive. (each board is about 9-1/2" long and 4" wide.) It may be that you can get the boards w/o the shifter, esp used.
http://www.cruiseraccessoriesonline.com/products/Valkyrie_Driver_Floorboards_with_Heel_Toe_Shifter-579-0.htmlThe biggest boards I know of for valk are Darryl's FX6 Customs. Looks like the boards are in front of the pegs. And you might have to remove the engine guards, which I would not do. Really, more of a highway peg/board, than control boards.
http://www.xf6-custom.com/partpages/floorboard.html