Yeah, pre-1967 440s had an issue with too small exhaust valves and resulted in heat issues, they enlarged them in 1968.
I found the plate. Maybe you can make sense of it. Lol.Totally agree with the lack of options, especially manual steering. On the inside of the driver side fender, on the flat part just under the hood should be one or two rectangle build plates to check everything and verify what the car was equipped with originally.This is not all inclusive, but tons of info on it. And yep, 440 automatic should have an 8.75 rear end( limited slip for the model, in 3.23, 3.54, or 3.91 most likely, the last probably for more racing), but the manual brakes and manual steering is rather rare to see, and 3speed windshield wipers to boot. GTX was the businessman high end performance car, so she is special if the fender tag is accurate with the "standard" things like PS and PB not on the plate, along with the bench seat and column shifter.
There may also be a build sheet located between the spring and padding of the rear seat to really nail everything the car has, removing the rear seat is not that difficult.
In your engine picture, to the right of the radiator hose where the sparkplug wires are crossing, is a flat pad, right behind the timing cover surface, with numbers and letters stamped into that pad so the originality of the engine in the car itself can be checked (besides the ones on the side of the block). There are several sites that give details on the numbers and what they mean, but it is always fun to help someone out with these, get to see a rare beast such as this.