This next step is one that can test your patience and even be a little intimidating, but it's really not too tough. There are two sets of roller bearings supporting both ends of the cluster that are separated by a spacer. Using regular high-temp wheel bearing grease, stick the first set into the end of the cluster and then push them far enough down with the spacer to make room for the next set. Put in another set of rollers followed by another spacer. Be generous with the grease. Make certain to put the long spacer in behind the first set before you grease the rest of the rollers into the other end. If you are using a new countershaft, cut the old one to the same length as the cluster and push it into the cluster so that it's flush on both ends. This will hold the bearings in place while you are installing everything into the case. Then, you can use the new countershaft to push out the old, and everything will stay put. If you are reusing your old shaft, slide it into place after the bearings are greased in just to make sure everything is in place. Then, slowly pull it out and carefully put the cluster in a freezer for a while. The extra cold grease should hold the bearings in place while you are juggling the cluster and main shaft in the case.