If you actually meant a 42rh not 46rh. No cutting of the floor required. All that is needed is to modify the cross member and remove the upper hoop. If you are gonna be running high HP, you're gonna run subframe connectors and reinforce what you take out of the upper hoop.
I did mean 46rh, but if I don't have to mod the floor with the 42rh then hell I'll do that :) remove the upper hoop? Like, the upper hoop in its entirety?
