I had to replace the tunnel in my 68 to fit a TKO600. I'm sure it's very similar to putting in a T56. When I got my trans kit from
www.hurst-drivelines.com they included a new tunnel patch. I'm sure you can buy one from them if you don't have the tools to make one. It was an easy install. I have pics in my build thread if you want to see some. I still have some cutting to do around the shifter opening but it's all been welded into place. I'm going to use rivet nuts and make a panel to close the opening up even more.