G'day Mile High!!
Beefing up?
If something has to be beefed up my understanding of the term is that for some reason it was not structurally sound enough at the first attempt. Not the same as a different design process.
With rear-mounted engines the wings tend to experience more bending moment. Lift force bends them upwards and in a conventional wing-podded design the engines bend them downwards.
Without podded engines the wing is cleaner but will experience more bending moment "M" unless someone does something about it. For simplicity sake imagine a wing beam to be a solid rectangle. Its moment of inertia "I" or ability to resist bending is proportional to breadth and the cube of depth. Stress "f" is inversely proportional to the distance "y" from the plane of no bending called the neutral axis. Which is smack in the middle for a uniform solid beam. And the radius of bending curvature "R" is inversely proportional to a mechanical property called Young's modulus or "E". For simple elastic design M/I = f/y = E/R giving the designer several options to counter, for example, increased bending moment without increased stress and/or physical bending without too much sacrifice of competitive edge in weight and aerodynamics. Not so easy at the tail however where you now apparently want to hang the engines.
Make all the due allowances for the shape of real wing spars and the stress engineer can work to some compromise with the aerodynamicist and obtain a slightly thicker wing perhaps which truth to tell was beginning to happen as successors to the peaky airfoils were developed. But at the tail end of the aircraft is a vanishing point and consequently both stressmen and aerodynamicists want to be slimming the shape down not bulking it up. Sadly the solution usually means stronger and heavier materials going into the tail than would otherwise have been put there... if that is where you want the engines to be. Building a physically stronger tail might allow you to do other things with it but certainly now that it is heavier every little trick to reduce drag is crucial not trivial.
Neither situation of wing and tail is really a beefing up more a penalty of going down the chosen design path. Richard "DC-9" Shevell was happy to admit Doneless wanted to look different from Boering and he acknowledged that there was also a thing called "fashion"!
My father went through both brain drain in forward and reverse, leaving de Havilland for Douglas where he freely admitted jumping from frying pan to fire, and then back, this time to Airbus to tear out what hair was left!
Significantly he was not a Tee-tail aft mounted engine proponent so make of that what you will. Airbi still have the 5.4 metre diameter fuselage and an invisible "sea anchor" holding 'em back but of course the spin on that is "optimisation". Not my words but my old man's - "Optimisation my a**se". Tacitly he envied Boering their better aerodynamic research and was scathing of what became known as the
[expletives deleted].
I happily plied along in Boering products and Lord do I miss feet up "smokoe" with the old chap. He had a great life, him and all those others, and in the days when your job title was written in your passport, dad's said "Rocket Scientist"!
Have fun! If this ramble has helped pass the time and learn a little good-oh. If not, well I'm old meself now.
The "E"