As luck would have it, I even saved the piece that I cut out, so I do not need to pull my carpet back to get the dimensions. I left the hole open and just covered it back over with the carpet since the carpet is naturally stiff as it goes over the edge. If you want to recover the hole, the simple way to do it would be to cut a piece of aluminum flashing and use some sheet metal screws to fix it in place, with a little caulk for a good seal.
I used my sabre saw with a coarse tooth wood blade. You will find that cutting fiberglass will kill a sabre saw blade, so use a coarse one. I was very relieved when the piece was cut out to see that it was the ideal size to cut out to access the coupler, at least on my CMC.
The width of the piece is 3.25". The hole is centered over the hump and I used a grease pencil to lay it out. A Sharpie would also work. As I recall, after laying it out, I drilled a hole on the top side to put my sabre saw blade into to start cutting. Picture 844 shows the piece from the side, in the same orientation that it would be on the car. The top dimension from the front of the seat to the edge of the curve, is 2.25". Those dimensions should do it for your surgery. I did not want to cut out more than necessary, and this small hole allowed me to get a wrench onto the coupler and the small set screw for the tranny shifter.
If you need any other information, let me know. Also, Richard, please write up any difficulties that you encounter moving the shift rod forward all the way to where the front tire usually sits. I know that my car does not have a hole in that area and you will probably have to use a hole saw in your drill to open up a place. I think that I will also have to replace the shifter bushing, so hope to benefit from your experience.