What's broke?

Since you don't really have to remove the cluster gear, the arbor tool will keep everything together. The tabs in the thrust bushings pretty much stay aligned if you just drop the cluster straight down, maybe use a couple alignment punches, you don't have to drop the cluster gear far, just enough to get the input shaft out and back in. As for the key, get it as close as you can, there is plenty of leeway, then tap the countershaft just under flush. Again, grease will keep the key in position untill it is in the pocket.