My Pertronix came with only one bracket, like your photo on the left. I can't explain the diagram on the right, showing two brackets.
An additional bracket would position the sensor higher, which might cause it to interfere with something. I doubt it is needed for e9 applications.
Yes, you should re-time after installing the Pertronix. I found that my carbureted 2800 started and performed better with a bit more advance, after installing the Pertronix.