pwnsummer wrote:So what would be best way to have both weapons on the model? just cut one of the arms off the biting blade?
That would leave two hands on the hilt, which would look out of place. The best way is probably to start with his Chainsword, and then lop the blade off and replace it with the one from the Biting Blade. A bit quick and dirty, and it'll only have enough room for him to use it one handed. But given his other hand is a massive claw he's not going to be two handing it anyway.
A better question would be why you'd do it, as the Claw does everything the Blade does and can get an extra attack from the chainsword. You'd be paying points to make the Exarch actively worse.