The Olds was easier than yours. I have your starter packed and will ship tomorrow. I hope you try it and let us know how it works. If it continues to run please be gentle on me in the forums. My reputation is at stake.
A rebuilder about 15 miles away asked me to come in today to look at a 6 volt 1954 Olds starter. After a number of others have looked at it and a new solenoid, guess what it still does. Stays running after key is released. Sounds familiar. Huh.