I would make the decision on which transmission you plan on ending up with before i would select a rear end with emphasis on the gear ratio.
A SM420 will need highway gears in the rear end. A T-5 will benefit greatly from a rearend ratio between 3.73 and 4.64, depending on the the overdrive ratio that comes in the T-5.
If the 5th gear ratio .86, a 3.73 rearend would likely be optimal.
It the 5th gear ratio .73, a ratio as high as 4.64 would be recommendable.
Keep in mind that you can dial in the setup by selecting a specific tire diameter.
I have a T-5 with a 2001 Nissan Xterra six lug (Chevy pattern) limited slip axle with a ratio of 4.64. I tweaked it into perfection by changing to 30.5" diameter tires.
With this set up, I can pull a tree stump, and drag it down the road at 80 MPH.
Did you have to have the Nissan hubs drilled for different studs? That’s an interesting option. Never knew they were 6 lug.
