In that case he has changed something since I bought my kit from him. At that time all he needed was the number of strings and the approximate height of the blind to determine the length of string. He sold a kit for shorter shades, which all of mine were, and a longer kit for longer depth shades. I guess the color of string was an option too.
Beyond that, you are on your own.
In addition to the string my shades needed a few new bushings, the root of the problem, not the string itself.
'04 Alpine Coach 36' MDDS