Well a press is the best thing to press out the old tube and press the new one in. But a torch can be used too, just have to be very careful not to over heat the u joint if you don't remove it. I just replace both halves on the 8 foot cutter I just bought, I didn't have a press at work so I just cut the old shaft off next to the yoke, then cut the tube that was inside the yoke with a torch and it fell out, I then heated the yoke pretty hot and placed the tube into the yoke, set the yoke on a 2x6 on the floor and hammered the tube in. You also have to be careful not to damage the tube end with the hammer if you do it this way. If I could have done this at home I would have removed the yoke from the ujoint and used the press to remove and replace. As for overlap most say at least 6" at minimum, I try to get as much as possible , while keeping enough slip to be able to remove the coupler from the pto shaft on the tractor, and not have any issues with the shaft bottoming out while hooked up.
