1989 RMX250 help

So a buddy of mine just picked up an '89 RMX 250. Like every other roached out bike he purchases, it is in my garage for what appears at first glance to be carb clean, top end, wheel bearings, linkage bearings, some crank seals and suspension freshened up. Probably a lot more when I start digging deeper.

My question is around the model designations specifically when searching the OEM parts diagrams. For instance when I am looking for carb parts I see 2 different carb models K/L/M/N or P/R/S/T. This is the case for multiple diagrams and I can tell that the carb on this bike is listed under the K/L/M/N diagram. Other diagrams are a little harder to discern differences.

What exactly is this designation? The bike has undergone a slight transformation from what I can tell as there is an RM rear fender on it and an RM front number plate, so all lighting has been removed at some point. I have no idea what else has been changed over the years so any assistance as to what these designations are would be a HUGE help.