Thanks for the link. I had missed that one.
Little of that build matches my intentions, but still... very interesting.
More cubes, more cam, more induction... heads with those flow numbers should be lively!

JFC, I think an alternative engine swap is more attractive all the time!

Some people just can't comprehend the effective difference between shooting into space and a shooting into close proximity to your own foot.

First, a thank you to the heavy hitter knowledge and experience that responded to my thread.
Especially Joe who consistently keeps it professional and sticks to the technical.

Re-read the first line of my OP... and consider why I may have been reluctant to even open the can of worms.
See, contrary to the status of "newbie" I am not new here. I actually participated on the old forum back before this one was even created.
I have witnessed how people behave. I quit reading this very forum over annoyance with the persistent pissing contests. The one that I would call the final straw involved individuals in this very thread. I am feeling like I may be headed in the same direction.

This "hobby" is pretty fragile. I have played long enough to see parts availability come and go. Choices were always limited from the beginning. So competing for business was also challenging.  A well known FE racer (I dont care to drop names) and I were discussing parts and I mentioned one FE specialist of the time (1970s) and the well known racer said "their stuff is a four letter word."
It was challenging then as it is now. The constant is that as a consumer, I am picky about who I deal with. Ross, while being understated, makes some good points on this.
End rant...

So back to cylinder head choices, from a shopping consumer and curious builder. Keeping in mind we aren't talking all out high rpm race stuff.
Joe's data is an interesting study.
Blair, are you asserting the BBM head might offer "more power under the curve" despite comparative flow numbers?
I am well aware that sometimes velocity Trumps raw flow numbers.

My mistake. I thought I saw an AFR FE head listing somewhere.

But OK, related question-
We have often dwelled on intake to exhaust flow ratio data. "Back in the day" it was often described as a common FE weakness and we often tried various ways to crutch them up...
Some modern builders have downplayed giving it too much attention.
But even more to the point, how much effect does putting these things in a Mustang with shock towers and headers with sharp turns at the port exit...
I guess my point is obvious. I feel there was very little benefit to the port work I did back in the late 70's when I was young and still breaking the chronic "more is better" habit. These 67 GT heads are pretty, but one of many minor mistakes.
This time around I want to research and get good value and a well matched balanced combination.
So good heads. How much money wasted choking with shock tower headers? The things look good with Dyno headers, but... maybe cheaper heads. Or maybe chop those towers out. Yikes. Very unusually solid S code car.

I guess I am a glutton for punishment.
I have installed/removed headers on my Mustang multiple times over the years. 3 different brands (I dont remember the names except the current Hooker Super Comps)
First was removal of the TRI-Y style that was on it when I bought it in the mid-70's. I then installed a set when I rebuilt the engine since it had been sitting in an impound lot for 9 years with the hood off and intake stolen.
I had transmission problems and had that thing together and apart too many times...
Got frustrated and decided the fix was to convert the C6 to a top loader. Well dont you know those headers were auto only. So along came the Hookers. Had those on and off a few times. Last time to address gasket issues.
I found the sharp edges of the weld bead at the tubes readily cut the gaskets and caused premature leaks. I "engineered" a fix and they stayed on for a long time.
I think I put in all the bolts in every time. GT heads.
I did the "custom bent" trick, and also ground the box end of my special wrench to thin it out a bit. The special sauce was before installation I located the tight spots where the wrench really wouldnt fit and very lightly dimpled the tube around the bolt area so the modified box end would fit on and off the bolt for final stage tightening. This helped a lot, but it's still a pain... (see my previous post on avoiding doing it in the car)

Edit- I just remembered the second set were from an obsolete brand Casler or similar. They were a sub-brand of a better known manufacturer.

For the record, the original image I referred to in my question was from Shelby American in the 1960's at their shop.
Thanks for the confirmation folks, it eases the dread having installed and removed the headers the hard way too many times.

Yeah, I understand that.
But in a modern day of 3D scanning and manufacturing potential, I would think it might outweigh the cost of an adapter and Cleveland option.
Though a very limited potential consumer base aggravates the situation.

That big flat torque curve though...