Here is a comparison of the T56 Magnum gearing vs the Toyota Supra Getrag V160. Notice the magnum's 4th gear is equivalent to the Supra 5th gear.
|Gear||V160||T56 Magnum "close"||T56 Magnum "wide"|
As you can see, the t56magnum gearing is a good bit lower than the V160, so to get V160 style gearing requires a higher rear gear. Anywhere from 4.00-4.30 would mate up perfectly to this transmission. If you have a 9" kit, then you have to just do a simple gear change.
The other option would be to swap to a TT auto rear end, this would get you to a 3.769 rear gear ratio which would be pretty decent. The other option would be to go to an NA Auto rear which would be 4.08 gearing, but not sure about how long that would hold up to power levels.
While changing out the rear gear is not required, I do recommend making the change to make street driving more pleasurable.
For my white Supra, I went with a "close" ratio magnum, and 4.28 rear gear. This almost identically matched up to the V160 overall gearing, but gave me a little longer first gear (YES!) and a little more top end in 4th (YES!)