Do you need the information for the standard cruiser configuration or for your cafe racer configuration? They are not the same.

For the cafe racer you'll either have to split your shock and measure the free length or call RYCA. It's probably best to just split the shock.

The rate of the spring would be "nice to know" but isn't really necessary to determine the correct spring rate. The cafe racers have fueled-up weight of about 325-330 pounds with a near 50:50 weight distribution (47:53) front to rear. The rider sits with a slight rear bias which will send the distribution further back. A 170 pound rider will bring the total weight in the neighborhood of 500 pounds with a 44:56 ratio, resulting in about 280 pounds on the rear axle.

That information, along with the free length, 13.5" eye-to-eye distance and 2 inch travel should get the shock supplier darn near the right figure.