I would never hack up my a1200 case since they are hard to find in the us if you screw it up.
If you don't mind buying from over here (australia) check out http://www.anythingamiga.com/amiga/cat50_1.htm
I reckon they used to make a few new 1200's in towers and sell the cases.
Sorry if anyone read this before. I had the wrong shop thats why i couldn't find them