The brain gives rise to the mind, in the same way that the physical computer, in operation, gives rise to abstract computational processes. Could you pinpoint these processes exactly in space/time? No. You can pause the computer and _inspect the state of the system_, but this not the same as pinpointing the _process itself_. The process does not exist inside the debugger.
Yet you can not say that these processes do not exist or that they don't have an (abstract) location. Assuming a non-distributed model, if you kill the physical computer, you also kill whatever emergent properties it has. The same is true for brain and mind.
"how many lightyears wide would you have to draw a box that contains all the physical processes necessary to simulate your brain "
Well - if you want to map physical processes to the locations of their abstractions, you could say 'the mind is in the brain'.
But if you posit your mind and brain are different things (and I think it's pragmatic to do so), then the mind does not have a location.
It doesn't matter 'what particles are where'.