Like I said, I tried every obvious deletion method:

In both standard and poly mode, deleted faces, edges, vertices.

Tried a boolean with a large box and the object to physically subtract half.

I would just start that part of the model over, but I have a feeling there is something very simple I'm missing in a slightly less obvious place, perhaps some form of locking mechanism built into maya that wasn't present in 3ds. I've run into other problems too: it seems random, but sometimes I won't be able to translate vertices at all, even though they are not locked.

So, perhaps it's due to the process I used to model it:

I lofted a bunch of nurbs curves and then converted to subd. Any possible way that could freeze anything up? It's quite strange.