How to Combine 8 N/8 FFT's into one N FFT
After giving it some thought I think I've come up with the answer. I was confused since most butterfly diagrams begin with 4 separate n/4 DFT's, like in the image below (annotations added).

Whereas in my problem I begin with 8 separate N/8 DFTs. I was confused about how to connect the outputs of each of the N/8 DFTs to recreate an N DFT. 

Now, however, I believe that nothing really changes between the butterfly diagram attached and my problem. I think that each output of my N/8 FFTs is directly fed into each input of on the diagram attached. And then the twiddle factors increase by a factor of 8 after each iteration. 

Does that sound correct?