Any good 350 short block should be able to handle 400hp/tq. If you can I would try to get a block with roller cam provisions, 4 bolt mains, and flat top pistons. Those three things will give you a great set up to build a strong engine down the road. If you can I'd also spring for 6" rods, a nodular or cast steel crank, and the best balance job you can get. A high volume oil pump is a cheap upgrade and while it may not be absolutely needed, it's cheap insurance. If you can afford it forged pistons with a thin ductile iron or steel ring set are also great.
Getting all of the things I recommended will set you back a good amount, keep in mind there is a BIG difference between a run of the mill reman enigne and a top notch custom built engine.
Going cheap isn't a crime, but if you want to get something really nice I'd look for the things I mentioned. A 3.75" stroke may be a consideration too.