Clean the bearing outside diameter and the crankcase with acetone, and install the bearing with a thin coat of JB WELD glue. Let it set up overnight, and have at it. I've seen JB WELD used to install cylinder sleeves in full size engines, so I'm sure it would hold. The engine will probably last forever and ever in an airplane, so don't worry about future changes of the bearing. Do check the bearing closely to see that it doesn't have any unwarranted internal play, and that it is a nice snug fit on the crank, but from what you describe it is loose in the case. When the engine warms up, the aluminum expands more than the steel bearing, and it gets looser. Also, it is fairly doubtful that you will get the seal out without damaging it. The seal is critical, as if it leaks air, it will lean the engine out. (NOT GOOD!)

Good Luck,
AV8TOR