You should be able to install the new bearings into the old tub. I've never done a Bosch bearing job. On the bearing jobs I've done, I pound out the old bearings and use them to tap in the new bearings. Put the new bearings in the freezer. Tap them in evenly as far as you can with a hammer. Use the old bearing and tap them in the rest of the way. Only tap on the outer race of the bearing.