defo RM because the mount bracket is welded to a plate welded to the chamber exactly like my suzuki pipes.
I cant quite determine the length of the rear part of the pipe.
I'm going to say 250 83D.
If it is a 250 Z or D it will have an indentation pressed in to it on the other side of the main chamber to clear the kickstart.
It could also be 465, hard to tell from that pic.