[Joe Rutledge]

I looked at the original engine last night, and I was not quite right. The two outer exhaust ports have the 4-bolt setup, the two inner ones have a 3-bolt setup, with the bottom bolt hole not being drilled. I am pretty sure about the ones on my engine, I do not think it is grime which is obscuring the bottom bolt holes.
I think the casting number was C7AE-A.

The original 428 / dual quad had very good street manners. It had the same hydraulic cam as a 390GT. It idled very well, pulled well low down. I remember I used to shift between 5400 & 5500 with the original 350 open rear. If your car had a non-productuion 428 PI (police interceptor) it may or may not have had the 390GT cam. There were some PI's in that era that had a solid cam. As long as the dual quads vacuum secondaries opened up properly, there was quite a rush when they kicked in. Initially flooring it gave you the rough equivalent of a 600cfm double pumper (two accelerator pumps) until the vacuum secs kicked in. Very very drivable - only a few situations where a single four was more responsive at lower RPM. I always felt that my car was about equal to my brothers friend's 69 CJ Mustang (after I removed the transverse muffler). The CJ was probably a little more powerful, but I think the 67 was a little lighter. At the dragstrip mine MPH'd a little more, my brothers was a little slower (105+ to 104+). The CJ squealed tires more when flooring it (advantage of single four).

I am pretty sure the exhaust manifolds were the same as a 390GT Mustang, there should be someone else who can confirm this. They made pretty good boat anchors for lake boats.

I do not really know anything about special or promotional vehicles of that era.