What about edelbrock cam. They are good quaility and work well in heavier cars.
Edelbrock.com - Power Package - Top End Kits - Chevy
Look at the power packages above. you will see one for 400 hp or round abouts. It may not suit your needs. But you can see what is out there with good heads and cams. 400 may be a stretch and still keep it running smooth.
I like the howards cam that was suggested as well. But may be a little small to make 400 hp and not as smooth as a good roller.
In this case i am going to recommend a roller cam. As you need all the low end you can get. Roller will give a clear advantage with heavier car and low rpm running.