Not too hard, remove the driveshaft and the speedo drive, then unbolt the tailshaft extension housing (4 bolts). Remove the rear seal, carefully collapse the bushing using a hammer and a "cape" chisel (has the angle ground from one side only, leaving a flat side that rides against the housing surface) and pull it out with needle nose pliers. Using the proper sized bushing driver (don't remember the size), install the new bushing so that it is about .010" below the seal surface. Check the fit with your driveshaft yoke to make sure things are good. Your yoke shouldn't be noticably worn or it should be replaced as well. Poke a wire through the rear seal drain-back port to make sure it's clear and install the new rear seal. Rub a bit of ATF on the seal and the bushing and reassemble.