Suzuki Cross Reference

Exhaust is pretty much specific to year...you'd have to go to PC or FMF and compare part numbers for each year to know for certain.

Go to partzilla.com and look up your bike and part. It doesn't work for all parts because something like a pipe may physically fit but might not cross over. Sometimes it goes backwards.In 1983 the hot set up for the RM250 was to put the 82 head on it bit you wouldn't find it called out that way. Anyway.click on the part number and a screen will come up saying what fits. With a bike that old though you need to do a lot of digging.

Cant say for the RM125, but I've fitted a 91 Fork/Triple clamps, 90 pipe (with home made brackets), 97 Keihin carb and even a 91 barrel and head to our 1989 RM250.

It's likely that newer model parts will fit, but often a case of trial and error with these bikes. And also how much modification/fabrication you are willing to do.

'89 was the first model year of a new redesign for that bike. The next "all new" RM125 did not appear until 1993, so your generation spans 1989-1992.
Most chassis parts will interchange from those model years. Be careful of the triple clamps, front wheel, axle, etc., because the '89 had conventional forks and the '90 got USDs. That tends to change everything up.

I had an '86 and an '88 and I swear the Suzuki engineers were taking a break those years. The two bikes were almost identical!