1979 series 3 exhaust

Hi I have a series 3 and I have just come back from a run and noticed the exhaust silencer box is blowing It has two silencers! done a quick search and found one but the question is there a difference in performance or is it ok to just put the one silencer on as a complete system ie no jetting change etc any tips would be appreciated as need to order one asap

One silencer should be fine, may be a bit more "throaty" but shouldn't need rejetting

Are you sure that there are two silencers?

One would probably be an expansion box and the other would be the silencer!

I've only got a straight through pipe to the back box behind the rear xmember - I thought this was standard?

Had a look in a couple o books and it seems to be a optional extra ordered the twin box one as that is whats on it should be a quick change lol