Eddie:
Use the kit parts as templates for cutting new bulkheads from sheet styrene. You will need to add the necessary details that are roughly shown on the kit parts like the doorways etc.
If you want to have the doorway open you can cut it out and build a door from styrene and show it in the open position. For the wiring harnesses and fuseboxes etc. you can make these out of thicker styrene either sheet or shaped styrene will work for this. For the wiring connections use either thin gauge wire or solder. For the other details in the area you can either make the necessary parts or find pieces for other sources (kids toys, spares box, fellow modeller etc.)
A reference I would suggest you pick up is the Osprey Series of modelling manuals Basic Aircraft Modelling and Advanced Aircraft Modelling these were originally released under the Compendium Publishing name. They're excellent books to have.
Secondly there was an article in FSM not to long ago on superdetailing a B-17 (Check the article list) As well you may want to grab a copy of the modelling Warbirds special issue from last year it has excellent articles as well on a B-17 superdetail project.
Let me know if you need more reference or more detailed instruction.
Cheers;
Gregory