Funny, on my 340 F/Sock engine, NHRA rates the iron head at 300 hp and the Eddy aluminum head at 297 hp. They are lighter but we have to add the weight back somewhere.
If just doing a valve job, keep them, unless you got money to burn. Downside, no hardened seat for the ex valve in stock form.
Compare both on paper, list all the good-bad points and cost for each. You'll see which way is best for YOU.
So the lower hp engine will actually run farther under the index than the iron head? Makes sense.
