GTI Exhaust

Just got a new exhaust system for my 83 1.8 GTI, just gone to fit it when I have noticed the rear silencer section is a different shape from the original system.
Does anyone know if there is a difference between a 1.6 and a 1.8 GTI rear section?
The one on the car is a flatter oval shape, where as the new one is round and has a smaller volume. Is this correct for a 1.8?

Yep, indeed the rear silencer is different between 1.6 and 1.8. Which one is which, I can't be 100% but I think the 1.8 is oval and the 1.6 the round one.

^correct