I'd love to see the next version of it, though, and see which of those schemes you end up going with!

If you're going to go with the one-sided mountain range thing, though, you might just want to have three plates -- the one in the north, the ocean one, and then a giant one containing the other two continents and starting to split apart where that bay is. I really do like the Gulf of California idea, still. Like this? (Now I've marked dark grey for inactive and red for active Cascades-style arc volcanism.)
Click image for larger version. 

Name:	Untitled-1.jpg 
Views:	162 
Size:	54.5 KB 
ID:	43326