I agree with Grumblebuns, check for chips/grindings by removing the magnetic drain (I think they were magnetic...could be the later ones), make sure it shifts okay, and turns okay, and put it in and try it. You might want to leak test it first too, as its much easier to replace the seals on the deck. These boxes are pretty bulletproof, my original has 130k on it, and I replaced it when 1st gear play was making a dull knocking sound at idle. It still shifts fine, though a little noisy in 5th gear (whine). Now it is my spare, but I measured the backlash on all of the case gears and they matched the newer box except for 1st gear (.010). I finally figured out that it only knocked because I had changed to an aluminum flywheel, have 3/4 cams, and the pinion gear bearing might have a little wear, explaining the 1st gear backlash. You can lengthen the rear shift linkage using 1 1/4 steel tubing.
Jerry Rude
4005R