I had contacted BedRug 4 years ago when I got my first 6.4’ Rambox. At that time I was told they will never make a BedRug for the 6.4’ bed. They do list 1 for a 5.7’, so I don’t know and wasn’t given any more information.
I had thought about just getting the 5.7’, but never did.
I had a BedRug in a 2003 Ram and really like it.
1st issue would be, yes, you could cut it. But for the regular bed, it’s shaped to fit around the wheel well humps. Probably could cut it if you just wanted to cover just the floor.
2nd issue would be if the ribs are the same or not. The BedRug fills in the ribs, so if they don’t line up, it will not lay flat. Again maybe you could trim them.
3rd would be once you cut it, the edges won’t be hemmed anymore. Not sure if that would be a problem though.
4th would be the Velcro strips won’t probably work out once you cut it.