4 speed Trans Tunnel mods

I have a 4 speed trans tunnel in my demon, has anyone put a 6 or 8speed Automatic trans in an A-body with a 4 speed tunnel. do i have to open any areas up or can it be left alone. I know i have to make a mount i just dont want to cut the floor. I will be happy running my 727 if need be.

let me know if anyone has done it. I have only ran 727 and 904s behind the gen 3's