I have a full Staintune system including a G/S style collector on my 1000 cc R80 G/S.
The conventional ,err, wisdom is that the G/S collector doesnt work with a 1000 cc motor, but mine works perfectly.
However, I have opened up the air box a bit, and the Staintune muffler probably flows a bit better than stock, so those that fit them to an otherwise stock bike may be disappointed, but you know about the air boxes already.