They did fire on the exhaust stroke until the V-Fire III was phased out, and up until the first Magneti-Marelli EFI (now Delphi) was used. Not any more.Harley motors also fire both cylinders on the same stroke where most other vtwins move the powerstroke to opposite ends of the 4 cycles... a big part of the unique sound of a harley is the bang/bang on the same revolution
You can retrofit an older model with a single fire system. You could even set up dual points if you want. The days of the "waste spark" have been gone for several years. If you like LOTS of spark, you can MSD your bike
You can get a Ducati to sound pretty much like an H-D, but the Ducati has a 90 deg. cylinder angle, and the H-D has the power limiting 45 deg. cylinder angle. Ducati's also have pretty large pistons, so you can just hear the displacement, as well as feel it resonate through your body. But then again, why would you want a Ducati to sound like a Harley?