I've found the easiest way to fillet grass carp is to have Duane (Carptracker) do it for you.
He's pretty handy with a knife. Even if it's filleting fish on the top of a cooler that is sitting on the tongue of the trailer, while getting gas at the station.....
I haven't decided if I like grassies better than bigheads. I'll need to do more testing. LOL.