check out
www.adperformance.com
Brain is a nice guy and can answer all your questions. I think he has 347 kits on sale for $899. Forged pistons, I beam rods, Scat crank, etc
IMO all the fuss about 347's being oil burners is total BS. Sure you can build a 331, but I really don't see a nickles worth of difference between the two motors