The 124 links that stainless refers to are the "dogbone" shaped links that connect the swingarm to the rocker. They run one each side of the shock, at the bottom. There are aftermarket links available of various lengths that lower the rear of the bike - I'm not familiar wit the gasser variants but the 124 will be referring to the distance between the holes. The longer the link, the lower the rear of the bike will sit.
Here is a general rule of thumb method for deciding if your rear spring is OK:
You've obviously sorted out how to measure it
so this is how you decide - adjust your preload ( the large rings) until you get a race sag of say 110mm. (lots of threads on this forum say up to 130? - the steep steering angle on the gasser allows you to get away with this) but just say 110 at this stage.
Now hop off the bike and measure the static sag (bikes own weight).
If the spring is correct for your weight, the static sag should be around 25-30mm. If the staic sag is more (50?mm in your case) it means you required buggar all preload on the spring for it to carry your weight, i.e it's too stiff. If the static sag was less then say 20mm, that would mean you have had to wind the preload up alot, for the spring to carry your weight, i.e it's too soft.
As a rule of thumb you can work on about 10mm per spring rate - for example on my bike to acheive a race sag of 105mm, the static was 40mm. The stock spring is 5.2, so this meant I needed to go 2 rates softer, to a 4.8 spring.
I went ahead and fitted a 4.8 and then I was able to get a race sag of 105 and the static was 25 - cool!!
Mate, I have to say it was the best thing I did - the front feels lighter, the rear feels softer, braking and traction are better, the front and rear action feels balanced, the bike feels like alive!
Both high speed and low speed compression clickers are wound out way soft.
Now the thing is, this is just what I've found works for me. It's different to the accepted preload idea around here - see the stickies - no one seems to want softer springs
Note, I only weigh around 150.
Hope that helps you some in trying to figure springs
Barry