That was a hot little engine in 1936! It worked great through the 60s and even made Yamaha copy it.
I still like 'em. I'll never forget the first time I pulled the head off my Triumph Tiger, pushed the kick starter through and saw the pistons come up together. I was sure something broke in the bottom end.
Years later, I learned about the concept of the twingle - a twin piston single engine and realized it was the natural evolution of the torquey singles of the thirties. Firing at 360 degree intervals was like mating two singles side-by side. It made for easy starting, had less mass and took less space than a V-twin and could be balanced to be smoother running. It was the perfect engine for light duty transportation before the car came along.
Those were great kinetic schematics. It does make one wonder why V-twins still exist. They are big with overhead valves and especially with overhead cams, vibrate without couterbalancing or rubber mounting, and don't cool well in-line. And all those different designs show you why they basically are not a good design. But, they sure are fun!!
Imagine a Guzzi-style V-twin with a 179 degree angle between the cylinders. Still a V-twin, no? Now, add a degree. Arguably not a V, but for the discussion of forces and vibration, the description of the flat twin as a V-twin can be made, IMO.
Inline fours don't balance too well either and their vibration tends to "grate" the human body more than a twin's does. Water cooling helps the issue of one cylinder behind the other and a twin's power output characteristics are arguably much more usable on the street. Right now I ride a V-four (I'd love to see some balancing schematics on that) but am thinking of switching to a big twin next. BTW, the most inherently balanced engine configuration out there is the inline six with 30 degree crank. That's why many luxury cars (BMW, Jaguar and, until they recently switched to counterbalanced V6's, Mercedes) use them. No counterbalancing required and they're smooth as silk!
The loping rythm of a V-twin is much more easy on the senses over long distances. Inline 4s can be very buzzy and don't most of them need balance shafts too?
My current stable of cars, trucks and motorcycles includes:
45 degree V twin
90 degree V twin
And yes there is nothing as creamy as an inline 6. It's a shame that Mercedes and Lexus have both dropped them in favor of V-6s. Mostly likely becuase v -6s can be produced on a V-8 production line and they are easier to package.