The driven in the pic is a stock unit. The shims are differential shims. There left overs from work I have done in the past.
Most shops throw them away so you should be able to get the from there trash or scrap bin.
It's cool to see some one else do it. Since it's a twin set up the work would be of great interest to others with twins.

Granted each spring as a pounds per inch, the pre-load, installed, compressed and run out height in way of poundage surprisingly has an effect. Used in conjunction with adjusting the drive a happy medium can be found. Before I always had to rely on a magic marker and a stop watch. With the a way to see the info. like a loggable set up like the vapor it took a lot of quess work out of it.

I had a tach however it would not show max and was only good for steady rpm on shift out, and required so fine tuned hearing.

Where I feel it pays off is for changing tire types, size etc as we as who you ride with where. A 28 hp (guess) pilot need every advantage it can. Pus it takes a good stretch to hit 60.

Look forward to you posting on results, putting 120 hp to the ground is not an easy task with a stock driven.

I had mentioned wore out plates between tran and Engine. These are a set from mine when I bought it used. I did replace with new and had to drill out trans for good tight fit and replace Engine/ trans bushings.

Had a little fun in the garage yesterday. Took some driven spring measurements and turned them into some data numbers. I do not have a spring checker so I used math to get the rate of the driven spring. Then I took four spring numbers and entered them into the spreed sheet. This will give me a base line for each. I now can add shims if I want to show change on a given spring. Since I have Ride Data with change info I can use that to dial in a given spring in combination with a drive unit for a given result. Yes, I did do the Drive as well however one item at a time to keep it simple to understand. This should shed some light on what I did in above posts.

If some one as an real life number for the spring using a spring check tool please post. It will show more accurate results.

The pic will show:
Rate
Free Length (spring just laying there)
Pre-load (Free Length compressed to Installed Height: Zero)
Installed Height (Zero)
1 to 1 ratio (ratio where the drive and driven are at the same Diameter)
Full Shift Out (were the driven pulley as expanded as far as it can)

Each springs free length is a variable since Zero,1 to 1 and Full Shift Out are fixed numbers based on the travel of the driven faces. The difference from the Installed height which is fixed and the Free Length is the pre-load. Since the Rate is Fixed.

This Pre-Load has an effect on belt squeeze at fixed points of the driven position.