Hi, Welcome to the board CH851SP3
If it was mine, I would make it my mission to convert it back to it's original state with original parts. It's probably why you got it so cheap.
A friend of mine had a 1977 900SS, blue and silver. Everything original. About 7 years ago he was about to sell it until a man in the know told him to hang on to it. In 2 years it doubled in price from €6000 to 12000. The same "man in know" also informed me that the 1991-2 S3 851 will do the same in about 5 years (2010) Why the 1992 model, because it was considered the best example of the 851 model before they went to the 888. If original it should have a white frame, white wheels and red mirrors.
Convert it back
you know you want to. Besides, riding a 851 masquerading as a 916 is like driving a TR7 pretending to be a Ferrari F40
See ebay article below
http://cgi.ebay.co.uk/ws/eBayISAPI.d...fromZR8QQfviZ1