Have cored my cans just recently, will post some pics and more tips shortly.
first remove cans from bike, wrap them in something to protect the outside.
1: look in to end of can, you will see 2 little welds.
2: with your dremel cut them through.
3: remove the inner end piece,
4: you will see two more brackets holding the end cap on, cut these.
5: with a little effort pull off the end cap.
6: slide the inner stainless can out of the aluminium surround.
7: cut off end of can with drop saw.
8. cut off as much as you can of the longest tube you see.
9: slide it all back together.
10: high temp silicon and some rivets to hold the stainless end to the can,
11: reassemble
12: go wake the neighbours.
Tips:
Careful with overtightening the exhaust clamps, put a bit of never seize on the bolts.
Before putting in those rivets have a look first to see that they will be hidden after reassembly.
If the inner end piece is still in good condition you can use it to quieten things down a bit by sticking it back in place
with a small rivet.
Some photos from "that other website" thanks to the nice person who posted them. They were a great help in visualising
what was inside.