Thinking outside the box
The problem, now, is finding a company that will gamble the R & D time and money on such an ambitious project for the L-A and Magnum engines...
With the economy in shambles and people abandoning drag racing like crazy I don't see much happening for the development of the LA/Magnum small blocks.
The 5.7L HEMIs are everywhere now and can be had pretty cheap which do not help matters any.
The standard EQ heads are cheap because there is a large market for cheap replacement stock type Magnum heads. They are competing against the factory Magnum heads (for stock replacement purposes), and the Mopar Performance R/T heads for the mild performance audience.
They bolt directly onto every Dodge Ram with the Magnum V8 engines that are extremely prone to cracking and for less money then a factory replacement or even a lot of the factory remanufactured/rebuilt heads. I'd be willing to bet this is where most of their sales come from and will continue to come from as these engines age.
Producing a 300 cfm head will only market a very small audience which means the price will be higher due to not as much demand/sales volume. The audience would be the extreme performance crowd as most (even a lot of the performance crowd) doesn't need (or won't buy, even though they say they will) that radical of a head. Being cast iron makes this worse because if people are spending money on heads they want aluminum, which will up the price even more.
Even if EQ (or anyone other bargain based company) produces "your" head (even in cast iron to keep their production costs down) don't think for a minute they are going to sell them to you cheap. A 300cfm out of the box Mopar head will cost $1,500.00+. Add in the mandatory custom manifold (~$450.00+) and 99% of people would be better off buying ported aluminum Edelbrocks.