Porting should be a good investment on an engine that big, even if you don't turn it much more than 4500 or 5000 rpm. I've used Hughes before for port work and they do a good job. I ran a set of their CNC ported Edelbrock heads on a 427 inch SB and it made excellent power. I wouldn't have any problem sending the heads to them. You should have them port match the intake manifold at the same time.