what is the difference?

[C G <justmecng2@yahoo.com>]

could someone tell me the difference between mg midget, k-3, mgb, and
roadster? if they are the same year are the parts interchangable? what
years and types exchangable with a 74 midget k-3? I am a new mg owner
i had a triumph 69 GT6+ now i have alot to learn about the mg  thank
you