Before I knew him a former boss and mentor had a '32 coupe with a Hemi mated to a '39 trans with an adapter. He had issues with the trans scattering on hard 1/2 shifts when racing. But he also had trouble with axle keys breaking. His "I'm a kid and know everything" solution to the key way issue was to polish the hub/axle/key way assembly to insure a tight as possible fit. His father was an old time welder/fabricator who basically told him it was a bad mistake. Of course the first time he jumped on it hard the key way held but the rest of the rear end not so much. He learned the hard way that it was easier to change an axle key than a complete rear end. Of course trans and rear ends were plentiful and relatively cheap in junk yards back then.