Not to step on Curtis's toes, or anyone else's for that matter but,

The 29-3E had the hardened yoke, and extended bearing surfaces on the yoke only. 29-4 had the self-adjusting yoke screw and the radiused stud package added. The 29-5's have all of the endurance upgrades such as the elongated bolt notch, larger cylinder stop bolt, and internal bolt block.