Well, I've dyno proven 14 RWHP by swapping rockers before. And I've also dyno proven 32 HP by swapping heads, and that was on an engine with a cam / fuel injection system that could take advantage of the swap.

50 HP for heads might be a tad optimistic unless you're planning on putting in a new cam, intake, and headers. Then again, I'm sure the heads I was starting with weren't nearly as bad as what these are, so who knows.