wow.
What did you use to clean it?
and for the dremel work, how did you proceed? how much of metal did you get of and on much places?
As above, the hardest part was removal of the bits, as most of it sits between the engine and the "firewall/cabin" so access space is limited. The job isn't too hard, just time consuming.
Once the manifold and EGR were off I soaked them overnight in a decent degreaser/engine cleaner to help remove some of the "gunk" and then attacked it with paint brushes and old tooth brushes till fairly clean.
With the dremel I ended up opening the holes to match the gasket (on the engine side) and just took a bit off on the EGR side. I did have quite a big pile of aluminium shavings at the end of it.
search google for "porting and polishing tips", just remember, rather take off too little than too much.