Wow, that's good g.plates work in there! Congrats.
SOLID WORK!

However, I actually think you went very far in the past which will complicate working out topography. And you saved this as a 520-frames GIF, which is a lot to work with.

Here's what I would do: save a couple of frames (but not as gif, since GIF-frames only contain changes from the previous frame), mainly from the last "eons". In each of those frames scribble where mountains are being created and where bits of ocean are getting trapped. You can use this detailed GIF you made to find that out.
From one frame to the other, carry this bit of information. But keeping in mind that mountains will erode and ocean floors fill with sediment, so that oldest notes "age"...

(did this advice make any sense?)