Mark, if I understood what you said, I picture the new space looking something like this. I see I missed the door in the upper right though.
Anyway, the way I have it, it looks like a 90x252 space with a 54x108 add-on in the upper left. Is this close? I also added a set of tracks with O54 curves (not shown) to the file just to get an idea of what the space will hold.