I found a shop that will do a complete drop in. He is doing one for my 58. The problem is the spring mounts, he will cut the old ones off the old rear end and reweld to the new. He must have the old to make the measurements to set the pinion angle.
The name is The Diff Shop, Inc. 1380 Ford St,Colorado Springs, CO. 80915 Phone 719-570-7830 Darold Boley.