First thing you need to do is use the search!......however as I'm in a good mood I've done it for you
1st useful hints and tips
viewtopic.php?f=10&t=40397&hilit=removing+the+plenum
2nd direct guide to remove
viewtopic.php?f=35&t=39226
You may need to do this while its off
viewtopic.php?f=10&t=50251&hilit=removing+the+plenum
This is the kind of graft you'll be putting in - expect a whole weekend approx 10 hours.
viewtopic.php?f=20&t=50059&hilit=plenum
Also a very good point Husky made to me when I said I was going to 'have a crack'.......its a Pringles moment when you start the Plenum - once you pop you can't stop......it'll look a bugger if you stop after a 'quick going over' - its the whole hog or nothing really.
Be more patient that I was too - no point gouging at it with wire wheel brushes other than for the initial de-burring otherwise you'll spend all day trying to sand the scoring out.
You will need a Dremel too.......no other make will cut it - it'll just burn out or fall to bits.