5.9 stock Mopar Performance Magnum with EQ Hughs heads HP?

Bobzilla said

Horsepower increase with this head swap without a camshaft change would not live up to the expectations that come with the expense of the new heads. The stock Magnum heads are not bad. Do a camshaft swap to maximise the heads you have and you'll be much happier. Camshaft and valve spring upgrade would really wake up that crate engine. Of your set on the head swap, wait until you can the change the camshaft at the same time.

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I was actually thinking of a camshaft upgrade at a later time but was also wondering if a piston change would be needed.
I'd like to be able to do whatever can be done with the block in the engine bay.
I'm not really set on the head swap but was just wondering what the performance increase might be. Jeez, I bet a camchaft and stiffer springs with no other changes could be done pretty cheaply but I'm curious how much gain could be had. Would be sooo much easier and be able to keep the street drivability.