Oven 3 Wire in Subpanel
For now, your bare wire's a neutral

Your oven branch circuit appears to have been run using a type SE cable -- this was common practice in the 50's as heavy gauge NM was not available at that time.  As the NEMA 10 is an ungrounded outlet with 2 hots and 1 neutral, the bare wire in your type SE cable lands to the subpanel's neutral bar.