I did the 727-to-Keisler manual conversion 2.5 years ago. I had clearance problems with the tunnel, and I even used an original 4-speed hump instead of a repop. If you do some searching on the web there seems to be tunnel clearance issues with a small percentage of E-bodies, mostly AAR Cudas. Not really sure why, or if the AAR thing is a coincedence. It could just be that so many cars have replacement floors (and other parts), which can have a lot of varaince in installation.
Once installed the transmission is great. When I bought my car it was almost undrivable. The engine was screaming at 50 mph, and I don't like automatics. This is way better/more fun to drive.