This is what I did:
1. Clean old header copper gaskets and exhaust ports.
2. Smear (thin) heat resistant silicone both sides.
3. Repeat with NEW copper gaskets as well as the old ones.
4. Slide flanges on pipes.
5. Fit pipes loosely into position starting the nuts only.
6. Silicon inside of muffler collector about 5-10mm inside. On all three pipes muffler end.
7. Fitting the muffler can be a gin....... You need to have this loose (no bolts)
Work out which header pipes are the closest in alignment, them wiggle
the header pipes and muffler until all three header pipes go in the collector.
8. Once this has been done bolt your muffler on and start tightening the header
pipes trying to keep the flanges parallel. Once you have the flanges firmed up
with a spanner (you won't get a socket on to the front bolt on the second port)
start her up give it a rev (blows excess silicon out, don't have your car parked
behind it as I did)......

got covered in silicone did not notice till the next day after it dried.
Get the pipes hot, let cool then retention the exhaust nuts.
Repeat twice more
NOTE:
You should not ride more than a few minutes without having the new tune put in
because you can run the risk of damaging the coating, be it ceramic or chrome.
This is pretty much how Nev Lush advised me to do....
Best of luck