I'm not sure exactly what you are trying to do, or what the book wants you to do.
But I can tell you how to remove a lid from a barrel.
All you need is a side grinder.
Stand your barrel on end.
Start grinding on the lip. Keep your grinder horizontal. Go around and around. Staying on the lip. after a little while you will see a fine line/crack forming.
Continue grinding and that crack will follow you all the way around the lip until the lid finally falls inside your barrel.
Very easy , it is rather noisy but it works fast and good. You end up with a round disk that is a perfect fit inside your barrel.
On A different note. Your RMH rocks! It looks great!
I loved this book. I bought the PDF and it was easy to read. There was a certain can do to this book which was great. It really helped me understand using rocket stoves. I built a rocket oven based on this book and it has turned out great. We have had many pizza parties and it has worked as intended.
The book also had information on making black ovens. I made a white oven.
It would be nice if the book had a updated version. As i believe rocket ovens made at WL are made a little bit different.
Illustrations were great. easy and straight forward to built with tims book.