My 87 SM800 was stolen in 2013 and found about 6 months later, destroyed. I have only the frame now. I always think, some day I will restore it. The fork missing is the killer. :)
A modern suspension fork is far better. However, these vintage bikes have a different ride than modern. The good thing is you can swap a modern fork in to ride and always put it back to original. Just keep in mind the rake/travel.. these bikes were intended with a certain travel.
what is the error you are getting? you can open the other cats?
http://vintagecannondale.com/year/1991/1991fr.pdf
http://vintagecannondale.com/year/1990/1990v2.pdf