331/347 are the same in price.
Without doing H/C/I and full exh dont waste your time. All that talk about the 347 and oil probs is long gone, they are as streetable as a 331. The 347 will net you atleast 15hp more. If you plan to throw boost on it, expect 500rw easily from 10psi and also expect to get a block that can handle it...some dudes are crazy and make 500rw+ on the stock block..man what nuts
With my basic 331, with small 1.90 heads, and small .498 cam, on 10psi I have gone 120+traps easy.