Just dowloaded it and got the model into maya.

I can see the problem! You need to delete the faces inside the model as they are stopping you joining the edges. I couldnt see the extra faces in the side view shot.
I've uploaded your model with the faces deleted and a vertice added to the edge as described. You should now be able to merge the required edges

Tip: Always check that there aren't any rogue faces around the edges you want to join.