AFR Heads

You might be right on the larger OD seat angle. If AFR had the 8mm guides installed at the foundry, they specified their own guide. If they specified their own guide they could also specify their own valve job.

Or, if they bought the heads with 11/32 and replaced the guides, they would have had to redo the valve job themselves. So either way a different valve job than SM is quite likely.

And I agree that the exhaust numbers are more representative of a minor port job. But you could also get there with a really good valve job and a tulip valve.