Jim,
Here is a usefull link to a site that gives pictures and dimensions on the T56.
http://www.sallee-chevrolet.com/BorgWarner/t56pics.html
I just checked and it doesn't include any width dimensions. If you like I can run a tape measure over mine.
I did the shifter mod to my T56 because the Australian T56 has a very rearward shifter location (more so than the one in the above link). I also did it because it was a bit of fun and a challenge. Half the fun and satisfaction of the Cobra (fir me at least) is the building of it.
Here is the shifter relocation thread.
Tremec T56 Shifter relocation
The Richmond box was out of my league pricewise and T56s come up regularly seccond hand. Mine had about 15000 miles on it and when I stripped it I found it was perfect inside.
Cheers