An SVA fail point was 104 db from the can (fireblade)
Taken the exhaust apart and the packing is in excellent nick with plenty of it.

Any tips on repacking it

here it is
Rescued attachment Vin Number 030.jpg

Repacking silencers is a complete bugger IMO. Too little = too loud, too much = too loud. We always use the wire wool type around the pipe then pack the type you have in your pic around it. Hard to describe how much to put in though.
Although I don't know what the conditions of the noise test are for the sva, make sure that the engine is warmed up before the test, that you keep the clutch in, never tell them what it actually revs to, make sure that there isn't a wall behind the exhaust for example for the sound to bounce straight back off and ensure that the bodywork (usually the rear wing in our case) isn't vibrating and adding to the racket. Usually works for us.
EDIT: Just remembered I've got some pics of one of our sportscar exhausts, I'll see if I can find them.

[Edited on 11/10/08 by Russ-Turner]

This is our new silencer, almost twice the size of the original one which failed our noise tests miserably, possibly due to our exhaust configuration. The wire wool pictured was a little too thick / tightly packed in hindsight because we were running 107db and the limit was 108db at the last circuit we were at. I think you can get noise testers on fleabay or at Maplins for about thirty / fourty quid if you want to try it at home.

[Edited on 11/10/08 by Russ-Turner]