The conversion isn't a hill I'd die on, it was sourced from a reddit economics thread as a bold assertion of fact:

https://old.reddit.com/r/AskEconomics/comments/q20fr4/the_fo...

The 1922 price list looks solid though, it's from a dedicated 1920s 'fan' site, but, again, I haven't personally verified or cross checked the numbers - it just seemed like an interesting bit of info to chase :)