David,
I just did a similar deal to a Triumph a few weeks ago. This guy shows up with a 1976 Triumph something and a Harley springer front end that he bought on E-bay. Harleys have a 1' stim and the Triumph had a 3/4 I think. Anyway long story short, he's going down the road now.
I would need to look at the two kaw parts but I think there is enough difference in the size of the stims that a bushing for both ends would be the easy way to go and just use the '91 stim. If not I could build the stim and upper bushing. The prices that you have do not seem out of line.
I will measure the offset on a 91 today and get back to you. I think if the trail and head angle are the same then the offset has to be the same, assuming the forks are the same length.