5-speed options
I think what Gene is talking about is that the modified TKO from Keisler is intended to fit without hacking the center out of your cross member.
My comments stem from what I have read about the problems people have had with their headers and a Keisler install, leading me to believe that the output shaft is lower than stock, even with the modified case. I can't say for certain that it is out of range, but to me it doesn't sound ideal. So, from that, I would say that to get the ideal driveshaft angle, even with the modified case, you still have to cut the cross member.
That said, if I had the money I would grab a kit from Keisler just for the modified case. I don't think it solves all the problems, so I would still be modifying the floor, but it would put me so much closer.