If you want to retain the suspension travel you have, here's my take on it:
People often refer to sliding the fork tubes up. Fair enough. Accurately determine Exactly how far you can slide the tubes up, without the tyre hitting any thing - noting if you still have Bar /Fork cap clearance. And you can usually, easily lift the bars a bit, if you have to, to get the last bit of tube sliding through, before tyre contact. Removable std HB mounts, can usually have a washer/ spacer added, to raise the mount a few mm, without losing retaining nut engagement. A thinner nut, with loctite to safely retain it, can give you that extra couple of mms. That gives you a good point to start at.
Then find a lowering link that will give you The Same drop in the height as the fork positioning will give you.
Match those 2 drops, and you don't stuff up the handling of the bike. Simple.
Some links , you may be able to get with adjust-ability - it may help if you like to change handling for courses, if you 'regard' the lowest fork height you can obtain as your 'constant'.
Lowering links do change suspension action - they can 'clock' the shock link, to change the arc of it's motion, and the rising rate through that change, they also change the CS / SA pivot, rear axle relationships. - and the swingarms static angle. Though, most people won't notice the changes / or, the changes do not 'go over the edge', into detrimental suspension geometry changes.
Another thing that can be useful, that many don't think of, is the height /aspect ratios of tyres. Fronts, there is not a huge range of difference - trying a 20" tyre is something I did, but, you are pretty limited in 20s for tyre selection. But rears, there is quite a variation. I'm not sure if the 2000 RM was a 19" rear - probably is. Going to an 18", gives you the opportunity to try lower aspect ratio 18" tyres - echoing the aspect ratio of 19" tyres. There can be a good drop in the rear height, going that route. But - research tyres before changing wheels, for aspect ratios available.
Every 1/2" you can get, is Quite a lot of height reduction. Picking a 'constant', or reference point for your height reduction, can make it all a hell of a lot easier in deciding your lowering methods. Just finding the lowest fork height you can Safely obtain, then trying tyre heights, can get a fair bit of height off a bike. You can achieve quite a bit of lowering, with minimal expenditure, whilst NOT buggering up the bikes suspension and handling.
Thinking, pays off.
