I did the 3.38 set in my 56. i got a new 3rd member from Hidden Valley Auto Parts and the R&P from eBay. i dropped all of this off at a transmission/axle shop where they rebuilt the assembly and swapped out the gears. I still used the truck during this time and saved a few bucks by telling the shop it was no rush and to do the job as fill-in work.
When it was all set it was a half day to change over the whole assembly. then I sold my original 3.90 3rd member to offset the cost
