Just cut the whole thing off and cap it
Hey Eric, I may be setting my car up for Factory Stock and was thinking of doing this but when I contacted NMRA tech, this is how they responded to my questions (there response is in red):
Stock unaltered frame- Can the front and/or rear crash bars be removed? Permanant portions of the frame cannot be modified or removed. Can the frame extensions forward of the radiator or passed the rear trunk line be trimmed off. Permanant portions of the frame cannot be modified or removed.
I'm not sure if that car is being built for a class, any thoughts on this?