TH400 is a bigger version of the TH350 (which is a 4/5th scale model of the TH400). It is longer which requires a shorter drive shaft. You also have to change the output yoke because the out put shaft of a TH400 is bigger and stronger (higher spline count).I didnt see anything about drive shafts? I just bought a 454 with a turbo 400 and plan on putting it in my 73 nova. I know i will need a different crossmember and i think a shorter drive shaft? I just got it so i not measured anything.