Well I got started on this today. My two barrels have the red liner. Only one was paint and the other was the tough as nails stuff. The painted one came right off with a good spray of oven cleaner (it literally wiped off clean) the other was not so lucky. Ill make that barrel the lower end which gets cut up anyway so there will be less to grind/burn away.
As for the cut of the lower drum, I found the following link
which prints a template for you based on your measurments, I did a quick test on some tin cans and it worked like a charm. (Note you need to check the scaling on your print out by putting a ruler up to the scale, I found mine was out by 10%)
One question for you guys, on the link I posted earlier for the t-shaped smoker, he has drilled a series of holes between the fire and the cooking chamber, Is there any benefit to this over cutting the hole right open and adding a defuser? I just cant see the benefit.