Morning! Thought I'd share my details. My exhaust seemed to be louder / raspier than I remembered so a repack seemed in order. Acoustifil mat ordered and pop riveter checked I dismantled the exhaust. The bad news was it was full of long glassfibre wadding still. The perforated pipe was also fixed inside the silencer body rather than the tail pipe which was removed, this meant a lot of fishing with a wire coat hanger to get the wadding out.

Getting the mat back in was harder until..... Two old cereal boxes , one rolled the same size (plus a bit) as the perforated pipe , then wrap the mat tightly, then other cereal box wrapped around the outside of the wadding, but smaller than the diameter of the silencer body. Then I was able to just slide the wadding down, I pushed the outer box down as well as it is smooth and stopped the wadding catching on the inside of the silencer body. Then just pull the cardboard out and job done .
Not tried running it yet....
PS wear a NBC suit when pulling the glass fibre out unless you like itching and scratching for a day :-(
Hope that helps anyone.

Next time try Rockwool insulation and ram it home with a piece of dowel.