Can I just use one end of a differential op-amp ? (ie use differential op-amp as a single ended op-amp)
You can just ignore one of the outputs if you only need a single ended output.  Leave it open.

It is rather an antique IC, something like 4O years old.  What characteristics of the amplifier are so good for your application?

You can't use it as a general purpose amplifier - it's bias current is high; its offset voltage is not very good.  You probably won't be able to use feedback without stability issues.

There are probably better ones available now.