We've done some 1990s SunTour replacements over the years. I ask the customer if they need to retain the shifters. If so then I am the bearing of bad news. As mentioned above ST used a different cog to cog spacing and thus the compatibility with current Shimano (and their clones) stuff isn't what we will suggest as it's not meant to work. If the customer can handle a different shifter (as in friction, thumb being the most common) then a shift lever and cog set replacement works. If the customer wants to retain indexing then a complete system swap to current stuff is needed. Then the cost is quoted and most fall back to the friction thumb lever option. Andy