Ive been researching SugarCane's M-Series on and off for years..it's 99% complete but still a bit of a work in progress..
First up are the 'MP' codes, from what i can gather they originated around the late 80's, there used to be some bits of helpful info on 90's era Japanese blog sites, Geocities and such, sadly nowadays its all been lost or archived...
MP-597
XX replica, redline denim, offset loop, what look like a boxy 50,s cut.
MP-603
Circa 90/91,