Eric,
The original exhaust system relied on the silencer clamp being tight, but the pipes had a bracket either from an upper cylinder base stud to the pipe, or one from the silencer clamp bolt to the lower subframe mounting bolt. Also, the original silencers had a boss on the side of the tailpipe to connect with the extra bracket on the Sports subframe. The silencers for the Mk3 Sports were longer in the barrel than those from the later models - also the tailpipe was longer and larger in diameter.
Regards,
Eddie.