A few billion years ago is plenty of time to plane things smooth. The collisions that formed the Appalachian mountains, for example, started a bit less than half a billion years ago and were mostly finished within a few hundred million years. Those mountains are pretty much eroded away now.

If you want to get a good example of a continental subduction zone, look at the point where the Indian subcontinent meets Eurasia (follow the coast along to the east and up to Japan for good examples of oceanic subduction). It's only a few tens of millions of years old and well underway. If you'd like to see a good example of a continental spreading area (a rift zone), look at East Africa, especially the Red Sea down through the Great Rift Valley.

For a good historic area similar to what you might be interested in, take a look at maps of North America during the cretaceous. There's a huge inland sea that slowly disappears over time. The PALEOMAP project ( http://www.scotese.com/ ) has a usable set of maps for looking at older world maps, but it's a very old site that may get cranky in the face of modern browsers.