looking to rebuild my 400 and would like some advise on improving the torque and horsepower

 

Lots of good stuff in the Stickies, might begin there.

Lots of stuff in the archives, too.

 

Depend on how thick your wallet is. First of all you want to raise the compression ratio in the 9 to 1 range.
Need new piston anyway check with www.tmeyerinc.com . He have the piston you need and much more. Change the cam for your application...daily driver, towing, race muding, street ,strip....A 4 brl intake, carb and headers to take advantage of those change with a straight-up timing chain. Don't be affraid to ask.

 

^^^^^X2 on what he said.....^^^^^ I think the most common is change out intake, carb get a bigger cam (RV type) and dual exhaust and you sir...will be amazed.