i wouldnt recommend putting any money at all in the heads. porting, valves, springs, nothing. dont get me wrong "magnums" are a cool piece. but by the time you spend $1500 you could have aluminum heads. advantages = lighter weight, better heat dissipation, better detonation resistance, etc.
investing money on porting / machining iron heads is not money well spent unless you need the iron heads for a certain racing bracket that requires them, or you are doing a 100% vehicle restoration.
the advantages of aluminum heads far outweigh using irons.
if you are set on using the magnums, i'd say use them "as is" until they fail.
