354 or 392? Hemi? Questions?

I'm going for it guys!!! I go pick up the hemi this weekend!! I am going to have to make sure it is what he is telling me it is!! So I found a website with the casting numbers. Is it still worth it if it's a 331?!? Also how much power can these things make? Say cam,intake,headers? I'm hoping at least 300hp 400 torque