Vintage Dirt Bike Q & A

I'm in the market for a 73-74 250 frame and found one at a bike junkyard but have some questions about it. The serial # correspondes to a 73-74 model (CR250M-10xxx), it has the welded on (from factory) exhaust hanger nut on the right side down buy the right peg and the welded on hoops for the exhaust springs (lower underside of frame). But, the right side frame upright (the one that comes up right in front of the air cleaner) is curved in and has a hanger welded on it, as if it was designed for an up pipe like a MT or MR. ?? Does this sound like a frame for an MR or MT?? Did the MR and MT models have the welded on nuts and hangers for the low pipe on the frames?? If it is a MR or MT what about the serial# being an M and not MR or MT???? I know in a pinch this frame will work but I would like to be sure before I buy it.
thanks