Originally Posted by T-Mar

While the fade paint scheme is atypical for Shogun of the era (usually they are one main colour with a contrasting head tube), I have seen one of these before. It had the friction version of Shimano New 600EX components. New 600EX was 1984-1987 but they came out with an SIS version that most manufacturers went spec'd in 1986-1987. Consequently, I was perplexed with what seemed to be 1984-1985 components on a frame having a paint scheme that was more typical of 1986-1987. The serial number was reported as 6505900, which I thought strange, as I had never seen a Shogun with a purely numeric serial number. Now, taking your serial number in account, it was likely S505900. The two serial numbers are close enough that the biycles are likely from the same production lot. Looking at the evidence from both bicycles, I'm strongly leaning towards a 1985 model.

You can see the other Shogun 800 and read the discussion here; Shogun 800 (and photo test)