I think there is quite a few people on here that have past the 300 barrior with no power adder. I did but i guess a stroker doesn't count Even though i had 342 which is still equivalent to over 1 rwhp for every cubic inch. I believe HairyCanary has over 300 rwhp also.
Now as far as iron heads i don't know of anybody but i think it can be done. Most people that have the money to for the good intake and cam go for the aluminum heads...
The work I did on Matt95GTS intake would be considered too much by some as it probably flows 240-250cfm. The best ported E7 heads I know of flow ~215 cfm. Getting the combo right is more important - and there are some "different" combos out there that work quite well.