What is the K'tinga? (Thats not a D7...)

Today we take an in depth look at a topic which has been bugging me for some time... the differences between the Klingon D7 Battlecruiser as seen in Star Trek The Original Series, and the K'tinga class battlecruisers that appear in Star Trek The Motion Picture. while the two classes are seen by most as merely interchangeable reskins there is in fact far more than meets the eye to these ships, their design evolution and their relation to one another...