K20a3 isnt going to make it to 400 without building it but I would highly suggest a k24 to reach your goals. You can even reach 400hp on a stock k24 block with out building the internals up. Just have to make sure you have good support mods and a good tune on your kpro.

http://www.ephatch.com/forum/showthr...l-Build/page28

Read through Monjarassis threads and you will find a plethora of golden infomation.