Fellow Sandgropers, for anyone wanting work done on their exhaust system, I want to give a huge plug to Peter at Exhaust World in Newcastle St West Perth. I went to him on the back of Ugame's comments about the work he did on his 916 GTV - great recommendation Chris!
He fabricated a new front half system for my '81 GTV (replaced everything between the manifold and the centre muffler) from much better quality steel to replace the thin, cracked and amateur-hour setup that was installed by a prior owner. Work included all new mounts front to back, as well as some reshaping of the rear end pipe, and raising the front end collector and pipework a couple of inches so that its now pretty much level with the sump (and no longer at risk from speed humps).
All done inside a day for less than $350. Can't ask for better than that.