Depends on the horsepower. I am using a 2002 4WD S10 Blazer rear end in my '39. It has the exact same hub to hub width as the stock rear end. I am using a 270 6-cylinder in mine with a T-5 transmission. I had to move the spring perches and replace with the narrower units. This rear end will hold up fine until you get into 350+ HP or so.
These diffs can take a lot of power. They're very stout.
