I'm planning on getting 350-400 HP. When will I start breaking parts? What parts will be the first to go? Can the 10 bolt rear ends handle that kinda power? What about the transmission? it's a 700r4. I'll probably put a higher stall converter on it and 3.73 gears. What are good parts to replace those with?

 

The transmission will probably be the first to go. I have seen the 7.5 10 rearend last in a car that was running 6.60 in the 1/8. You could probably put another posi unit,gear, new axles,have the axle tubes welded to the center section, and a TA rearend cover and be fine. But if you ever use a transbrake that is when the 7.5 will break. It will be hitting the rearend just like a manual car would and snap something.