Disappointed magnum head flow numbers....

Google Stan Weiss cylinder head flow data. He has results from about a thousand flowbench tests for just about any kind of performance engine.
From a cursory look at the LA section, looks like iron magnums look like 225 cfm stock, 250-260 ported.
Now for personal opinion. If you want to play with learning to port (or even if you are not a novice), work on a set of magnums that you know are not cracked. I doubt that i would pay someone else to port used iron heads. I would rather put that money toward a set of aluminum that already flows better than a ported set of iron.