Like Frank50 says , this is a good easy swap for your truck ,
I have a '55 diff in my '40 .
The spring mount is completely different as you will see when you examine them . But easy to build.
Important part is having the diff pinion at the correct angle to the trans output shaft.
After you have the new diff in , you will find the rear brakes will lock up cause they are Bendix , and you have Huck brakes on the front of your '48 . You will need to fit Bendix brakes to the front as well , for safety.
I did this after a nasty scare with the trailer on ,, works well now.
Look in the tech tips section .
edit , here is the link.
http://www.stovebolt.com/techtips/55rear.htm
