Everyone I knew back in the day shunned the 6 pack rods. Too heavy and no benefit. Those that ran the 6 pack rods broker or spun bearings. H beams are a much better route to go. I agree with others on the quench idea. IF you go with iron heads and have to go with the 906 heads, then get pistons with popups in the quench area so you can run street gas and not worry about detonation. Keith Black has these pistons and I am sure other do as well.
I have a buddy that runs a 440 .030 over stock stroke, with 440 rods and upgraded rod bolts. He runs a MP cam and small shot of nitrous with an automatic and 3.90 rear gear. He routinely runs mid 6 range in a full body 70 Challenger street car. AVOID the 6 pack rods like the plague.
Just my 2 cents worth.
You can spend some time this winter and open the 906 heads up to flow some really good numbers.
Good luck with your build.
Jerry