Found the 29 cells without much trouble but just can't see how they're connected to the 12 extra words or how they can be assigned to three groups of four? I didn't need them for the 29 cells but it would still be nice to understand them.
Also ...
36d - Capital of African nation relocating half southwards (4) ?IMA
There is an obvious "capital" but it's not in Africa and I've already got 12 extra words and can't match it to "relocating half southwards"?