Coal-to-oil conversion (1920)

By the end of 1920, 68 locomotives had been converted to burn oil instead of coal. There were still 26 locomotives still burning coal though.
[Source: T&P annual report]

Hello there. I'm volunteering down at the T&P Rail Museum in Marshall, Texas, and these are the sort of facts I'd love to find out to add to our tours. Do you mind sharing some of your research tips and resources?