Sorry, I've been out of town. But you folks have been busy.
Too bad the old forum discussions have been lost. probably why I couldn't find any references to the YB-40 on the CFS2 forum. Seems like it would have been discussed at some point. However, I still think the plane was never created for this sim or any others. It doesn't even show up as a CFS3, FSX, or FS2004 plane on the ususal sites (flightsim, avsim, simviation etc...).
I'm lousy at making planes. But I had the same thought you have about the place to start...a B-17G since the chin turret is already there.
Imagine if someone did create a YB-40, how difficult it would be to attack in CFS2 with the standard settings in the game for the gunners. It's bad enough how accurate the Val back seat gunners are. You would need to tone those boys down a bit to reflect reality, but oh the tracer would put on a show.