I would highly recommend the "rectangle port" heads you speak of.
I recently put the finishing touches on my latest 454, actually a .30 over. I prted and polished the heads to improve flow.
With a few other goodies I achieved a naturally aspirated 630 hp. Not the greatest number in the world but its as solid a motor as I have ever seen. Forged bottom end and all. After porting and polishing I gained 27hp.