Offhand I don't see an "M" code for the FE engine when reading the link posted (cool btw!) for the 58-59 vin id. Maybe it's a Y block possibly?? I have W for the 58 and 59 361 and B for the 59 352. I'm far from a Y block buff just a guess on the M. Also it's possible a FE was swapped into as this is a popular change some make if you have verified the engine family already. G.