B-17 cockpit pictures aren't showing me the same resemblance with the big trim wheels you see in the 707, 727, 737, etc. I do see them in the KC-135, Dehavilland Comet, etc.

There's a very obvious shared design between the 707 and 737 cockpit that goes beyond anything you could attribute to general cockpit design.

https://i.pinimg.com/originals/1b/67/96/1b67964cc0e7c178bb8b... (707)

https://cdn.jetphotos.com/full/6/22047_1484863414.jpg (737-200)

A300:

https://airbus-h.assetsadobe2.com/is/image/content/dam/chann...

It has trimwheels.

Sure. This all rolls up to me saying that the design of the 737 might have dated back further than the 1960's. I feel like the 707 is evidence that it dates back to the 1950's. It shares more in common than the 737 than just the trim wheels. That was just an obvious call out since there's an MCAS tie in there. For example, the 707, 727, 737, and 757 all have the same fuselage circumference.

As I recall, the 707-727-737 are a direct evolutionary line serving the same niche, and the 757 was intended as a 'stretch 727', so yeah, I think you're right.

Similarly, when I consulted with one of the major airlines (although not in flight operations) I was told that many of the physical specifications of airplanes were driven/limited by airport gates. That is, wingspans, fuselage curvature, door height, etc. need to be within certain ranges so that it could use existing gates unmodified. This was one of the biggest issues with adoption of the Airbus A380...airports had to build new gates just to support them. I understand that is an issue with the 737-MAX: to place the much larger engines in a place that wouldn't screw up the balance (e.g. under the wings instead of out in front of them) would make the plane inconveniently high off the ground.

707, 727, and 737 all share the same “41 section”. The 757 and 767 also share a common 41 section but don’t have any commonality with the earlier models. The latter two were designed at the same time, with Boeing using some risk management strategies: They used “new fangled computers” to aid in the design of the 57 wing, and the old way for the 67. The 57 wing turned out much better than predicted.

Maybe expound on this a little? Considering the 757 was (am I wrong?) a medium body short/medium haul airframe, and the 767 was a wide body medium/long haul, how are they all related?

The 757 and 767 were designed at the same time and have a common type rating. It’s not unusual at an airline that has both aircraft for a pilot to be flying a 757 one day and a 767 the next.