The Turbo 400 is not an overdrive transmission. I've yet to find anyone who has put another type of automatic with overdrive behind the V6( not that it can't be done). I have a Manual behind mine.
Over on the other Board (and he might even be on this one here as well);
AT Rockdriller put a 351E with a turbo 400 into his truck. His is a 4x4 but he made it work so I'd think a 2wd would be easier.
Here's a link to his build:
http://67-72chevytrucks.com/vboard/s...d.php?t=453161