Thanks a lot for the answers. My intention is to put only one muffler which would replace the original silencer, but that main pipe (or those two coming from cylinders, becoming one before the silencer) would remain as it is. I don't know about fasteners, do they match etc., but this isn't the biggest of all problems. (Gosh, this limited vocabulary makes troubles). The seller of the silencers will get rid of both and I don't mind buying both, maybe some day someone needs one and I am able to help. Well, best is to go and take a look of silencers. And first visit my bike, which is wintering some miles away, and measure a bit, so there will be so much room for speculation. The other way to proceed is to wish new muffler from Santa, who lives nearby, so have I heard.