SunTour made a real effort with their 1987 range. To support index shifting the XC 9000 got two sprung pivots. The quality of finish was improved from the old XC series, in particular the branding on the outer parallelogram plate cage was tougher and possibly lasted more than 5 seconds. The overall effect was more composed and integrated.
None of this made much difference. In 1987 the new game in town was indexing. Accurate indexing requires an optimised system involving all the transmission components, and SunTour had not managed to optimise the chain, freewheels, levers, inner cable or cable outer - and because of this the XC 9000 never indexed reliably.
This is a long pulley cage version - there is, supposedly, also a shorter cage version (model number XC00-GT) - although I can’t say that I have ever seen one.