If I understand correctly the Mythic Dawn is the end of one kalpa and the beginning of another.Also that when the tribunal in Morrowind used Lorkans heart they were sent (or became part of) the Mythic Dawn.

My question is which one A) The previous Kalpa to this one. or B)This Kalpa to the next.

If my grasp of things are off be kind but please let me know .

The Mythic Dawn is a group of Mehrunes Dagon Worshippers who want to be immortal like the Daedra, and have been fooled into believing that Mehrunes Dagon conquering Tamriel will achieve this end. The Kalpa's are cycles of Universal death and rebirth that are linked to Akatosh/Auri-El/Alduin. In the current Kalpa the destruction cycle was halted by the actions of Shor/Lorkan/Shezzar, and by treaties with Akatosh. The Tribunals power came from tapping into the heart of Lorkhan using Kagrenacs Tools. They are related events, but not in the way you are thinking.

I think you're confusing the Dawn Era, a time during which many gods walked on earth and controlled the events in time, and the Mythic Dawn, a cult which desires to bring about the return of this period and walk Mundus like its gods did in the Dawn.

The Tribunal broke the Dragon, bringing about the state of the Dawn again in which gods controlled events in time. The gods in this case being the Tribunal. It didn't last though.

I'm not sure how you come up with the Kalpas.

If we're going by the Aldudagga and Shor-Son-of-Shor the current Kalpa never ended. It was about to end when the Greedy Man made it so that there was more then Alduin could eat. I would assume he did this by making Mundus.