I may have a potential explanation for you Glen.
This is a pic of TKO dimensions from Tremec. Very similar to the dimensions CSX2345 shared with us. Tremec’s TKO dimensional data below has some additional image data; sadly, without dimensional specifics, which the Holley dimensions also do not provide.
The “C” dimension represents snout-to-mount dimensions for Tremec’s as delivered TKO tailshaft mount, as described by the “C” dimension in the graphic above. The “D” dimension is simply the OAL of the box. In Tremec’s dimensions table, there is approximately an 8-inch difference between the two.
Towards the rear of Tremec’s TKO drawing above, there is an undimensioned mounting location that most of us chose not to use, in fact, many of us cut it off. Kirkham used this mount in some of their cars and built what looks like a typically nice Kirkham billet aluminum mount to support the TKO tailshaft.
Here is a picture of that Tremec mounting boss being cut off by guys like us;
I have not been able to find dimensions for this mount other than to estimate from the Tremec spec that showed the distance from the frontmost mount to the back of the tailshaft to be 8 inches. That would put the front mounting point for that rear mount about 4 inches back from the front-most mount, which I think you may be using.
If you re-position your transmission engine package to use the rearmost mounting position of the TKO transmission’s tailshaft mount, you are going to move your engine/transmission package forward about 4 inches — essentially what you are looking for. That’s the good news.
The bad news has several components. The first is you will move your center of gravity forward, which will make the rear of the car lighter. The second is you don’t have the corresponding mount on the TKX tailshaft, which means some transmission crossmember fancy footwork to make everything fit the way you want it will be required.
FWIW this is what the Kirkham Mount looked like back in the day;
I would think if you intended to go this route (and had a TKO), Kirkham would be the best solution you could buy — but of course, that is not in the cards.
Because the TKX no longer provides the rear-most mount that the TKO had, you are basically back in the same pickle. One way out would be to position your engine transmission package so as to allow the TKX shifter to exit the transmission tunnel in your current opening the way you would like.
Once you have established the correct engine/transmission package placement in your car, you will want to build an appropriately robust tailshaft mounting pad on the chassis cross member so that the mounting bolt holes line up with the corresponding tailshaft mount bolt holes.
This kind of modification may also require some TLC be given to the chassis engine mounts. I am unfamiliar with your chassis, so I am not really qualified to comment on that or whether it would even be necessary. Again, because of my lack of familiarity with your chassis, you may also discover your headers will need some of that same TLC to exit the car in the proper location and manner.