H:\Steam\SteamApps\common\Sid Meier's Civilization IV Beyond the Sword\Beyond the Sword\Mods\Caveman2Cosmos
Path is bit lengthy, change Sid Meier's Civilization IV Beyond the Sword to just Civilization IV.
That path is not too long.
Since he is using v38.5 he must not delete the UserSettings folder as that version of C2C cannot recreate the folders, only later SVN version can do that.
However, inside the UserSetting folder there can be a file called "BUG Main Interface.ini" which, if it was created without PPIO, should be deleted if it's there before playing with PPIO.
Other than that, changing fonts and font sizes should be as easy as editing:
H:\Steam\SteamApps\common\Sid Meier's Civilization IV Beyond the Sword\Beyond the Sword\Mods\Caveman2Cosmos\Resource\Theme\C2CTheme_Custom.thm
Serif type fonts are mostly the only fonts that have all the symbols that the game require, using the correct name for the font in the .thm file can be tricky to get right in some cases.
The font must be installed on your system for the game to find it.
Some font types simply don't work at all, and the game will revert to a default system font.
Try first to change all the font sizes to 24 just to check if the editing is actually working for you, it should be obvious in game if you did it correctly..