"It incorporated a parking pawl when the selector was placed in reverse with the engine off, although there was no separate Park position." from Wikipedia
Thanks for that bit of information. I like learning something new every day, and I just did. My parents owned a 48 Olds with a Hyrdamatic for 13 years and a 52 Olds for another 2-3. They always left the cars in neutral with the hand brake on. I'm sure they never knew about the reverse locking feature.