If you want a good resource to research your Rossin's model you could go to this site:
"Vintage Rossin Archive" and I think this is the URL:
http://rossinproject.blogspot.com/
I too think it is a mid to late 80's model and probably Columbus SL/SLX. I've 'got my money' on SLX. I also think it may be a Rosin Record model?
Very nice find too. I wonder if the rear brake cable guides were removed to make it into a fixed wheel "Fixie"? Probably with only a front brake fitted?