I rebuilt my first 400 a few years ago. As said above the 400 and 350 aren`t difficult. And you learn much if you`ve never "been" inside a AT before. So go for it. Heynes book is great to follow. Dont think i needed any special tools for the 400 exept measuring gages and torque wrench (+ some thin walled sockets)
I spent lots of time making sure everything was right the first time.Was very pleased (+ saved $US 2000 wich it what a rebuild costs here in Norway)

Ian