RPO stands for Regular Production Option, and when filled in denotes some change from the standard fitment for that car that was done at the factory. The most commonly seen one is 333, which identifies a panel van with rear glass fitted. There are others for things like heavy duty electricals, door-pulls, as well as the seriously irregular
ones like one-door postie van etc.
However, because these things were hand-stamped, it's extremely common to see the second paint number more or less next to the RPO title, especially on FEs and early FCs. Later FCs have 3 fields for PAINT, INSERT, and TOP, but the early ones just have 2 sets of numbers stamped next to the word PAINT. (The word TOP does appear at the bottom right, but wasn't ever used TTBOMK).
In other words your RPO is actually your roof colour of 207 (Metallic Duco) - 7445 (Bermuda Green). Amazing isn't it? I don't recall Bermuda Green being mentioned on this forum in the last 3 years, and yet all of a sudden it's all over the place!
Hope that helps.
RET