RM 125 suspension upgrade

The best suspension will be one that is sprung and valved for your weight, riding ability, riding type, and track conditions, that might be the rebuilt 2003 OEM suspension. Bushes, seals and oil is cheap.

Yes a 2008 front end would be an upgrade in many ways. The forks are better and are still considered good against most modern day forks, parts are still easily available and most tuners have good settings for the 08 model fork.

I believe the clamp offset is different (less) and the top mount features rubber mounted bars.

You will need to buy a new front brake line as the 08 fork doesn't support the under fork foot routing of the 2003. But this is also an improvement as its lighter, looks better and gives slightly better braking performance. You will also need to get new fork guards with the modern brake hose attachment (and a clamp). If you get the latest RM forks with the metal rings, you can ditch the nasty plastic fork guard guides which saves further weight and fork stiction.

You are a bit stuck with the rear shock as it's a different length to the 04+ RM shocks. But a good tuner will be able to get it working well (if it isn't already)

Yeah, Suzuki updated the linkage for 04 and changed the shock to suit

Anyone know of any databases that would show rear shock length?

Was wondering this about an older model, 1998 specifically.

MX Tech makes forks and a shock for the rm. That would be the best route but its expensive.