Ian,
Thank you for the updates especially on the exhausts. I'd not seen a set of pictures of the internals of the OE pipe so that front section mesh pic was particularly interesting. I haven't seen the internals of the Delkevic repro but somewhere I believe I read that the mesh is not present and is the main cause of the expansion pipe sound. Food for thought there :-)
I do remember the Piper 3:1, they really did/do sound great. A fellow in the KK has one fitted, I believe. I bought one for my GT380B way back in about 1980 from a place in Erith, Kent, UK, but it didn't fit (or rather, I couldn't fit it!) and they took it back.
There is a set of the finned covers on ebay:
http://www.ebay.co.uk/itm/GT750-Suzuki- ... 1c3a414370
Enjoyed the read, thanks again,
Mike