You had me interested Dave so I looked online and found there is indeed an open gap ahead of the instrument panel. I guess this made it easy to access the various instruments for servicing and aid cooling of the electrics. Of course the various instruments would actually poke out the back, if you have seen particularly older ones they are very large and heavy items. There would also be wiring back there as you suggest.
Check this series of photos:
Check this series of photos:
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