Depends Upon Your Intended Use Also
Also depends upon what 6th gear you have in your T56. Changing the tire size (diameter) will also make a smaller difference. The problem with SOME T56 trannys is that they employ a very high top gear with a big gap between 5th and 6th.
This makes it awkward to gear the rear end properly. If you are willing to sacrifice some reduced cruising rpm at 70 or 80 mph, then, like already said so well, just go with a 3.73 or even a 4.10. However, depending again on the 1st gear...
...of your T56, your starting or 1st gear may be too short for drag racing, but would be OK for the street. Everything must be a compromise. My personal opinion is that the factory gearing (3.42?) MAY be too tall with the .50 6th gear?? Dunno. HB of CJ (old coot)