x vs j
From what I have been understanding for a while now on the heads are there the same minus the valve (intake) that was installed as OE.
Now, what is under the valve, as cast and then installed on a engine may be a different story. That is why I ask/mention that.
From what head porters have told me, the smog year heads flow a little less due to port reshapeing. But potentail is there for some super smokin numbers if need be.
More work than a letter head? IDK. I'm not a porter, I have no flow bench.
Talk to a porter.