I bought the wide ratio T56 Magnum for my G3 swap. Mostly because the ratio's match what my '15 Challenger R/T had and I loved how that drove.
The narrow ratio box have a 0.63:1 6th gear while my 6th is 0.5:1. The narrow ratio box is great with a deeper rear gear, but because 6th is deeper as well, it cruises at an even higher rpm. At the same time, with a carb'ed motor the .05:1 6th might be too much. I expect to cruise at about 1500 rpm at 65mph.