Is it possible to use half of a LM13600 instead of a CA3080?
ABSOLUTELY!

The LM13600 and LM13700 started out life as a practice piece for a new mask designer.  They were thinking about second-sourcing the CA3080, and the new 16-pin package made a dual CA3080 an easy exercise (just flip the layout to do the other side).  They had a few pins left over, so they added the Darlington buffers and the predistortion diodes.

The key takeaway is that the LM13600 and the LM13700 are both dual CA3080s with a little something extra added, that you don't have to use if you don't want to.

Details here.