For the technology group mapping, it look like the current system relies only on technological advancement of nations in CK2, and the Western technology group is assigned to most advanced nations from CK2 relatively to other nations (the absolute value of advancement does not matter) and the lower groups are assigned accordingly. For my conversion system worked fine when I converted game from end-game period (1453), my nations with Byzantium got Western tech group, while France that was fairly behind in technology got Eastern. But this system produces strange results if game is converted out of box from 769/867 bookmark, but for me it's fine, as it was designed to continue game from 1444. And I like the fact that the system rewards your investments into technology development, rather than being culture-based.