Rm 250 suspension upgrade

I can sell you a 2004 rm125 showa shock and I also have a spare clevis off a 2002 that will make the shock work with your linkage.

In fact, I can also sell you an entire 2002 rm125 showa shock, but it will need rebuilt

Your best investment would be to send the suspension out to the reputable suspension tuner for service and revalve.

I dont know how much different the 01 stuff is compared to the 07 but I had an 07 and once it was sprung and valved for my weight it was pretty damn good. The only dissapointment I had was when I rode a mates SSS suspended yz that was sprung and valved for someone my weight

It is totally different.
2001 uses Bladder Type 46mm KYB forks. 04+ runs on 48mm Twin Chamber Showa's.
The problem is, you cannot just bolt on the 2004+ forks and shock to a 2001 chassis.

Up front: Different triple clamps offset, different fork tubes diameter etc.
In the back: Different geometry/linkage, different shock.

Unless you want to spend a crazy amount of money on this bike, get a decent suspension company to revalve the stock KYB suspension for you and you should be more than happy with the results. Especially since it's been sitting in the barn for so long, it needs the suspension service anyway.

Imo the showa shock is better than the kyb, it has a much bigger piston.

I have a complete shock and all the parts and optional springs that could get you setup

All the wheels, brake etc is direct swap out

A well tuned kyb shock is just fine. Pleanty of fast mx'ers at the pro level rode that in the day. Get the linkage services, and shock tuned, and spend the $ upgrading forks if you want. Btw, they can also be tuned as well.