I've only had one of those early Ford rear ends apart and I don't remember exactly how it was built. It may have a solid pinion bearing spacer instead of a crush spacer. If it does then you might need some shims for it. If it has a crush spacer be sure that you use a new one. Also use a new pinion nut and put some red Locktite on it when you do the final assembly.
Be sure that you check the backlash BEFORE you disassemble it. Also use some gear marking compound and check the pattern BEFORE you disassemble it. Take pictures of the pattern so you will know what it looks like when you put it back together. You can get the yellow gear marking compound at a GM dealer, or from Randy's Ring & Pinion, Tom's Differentials or DTS. This works better than grease and MUCH better than the blue stuff that some people use.