Opposed Piston Engine: Apparently it can have better thermodynamic properties which leads to better fuel efficiency. There are a bunch of different tradeoffs with maintenance and engine size too, but it really depends on the specific applications
As you delve into the wonderful world of frame geomotry and construction, you will encounter two terms over and over: rigid and softail. You will also hear the phrase 'hardtail', which is the same description of a 'rigid frame'.
When you get into the discussion of motorcycle frames and what to build for your next bike building project you first need to decide what kind of motorcycle you want to build. Whether you want to build a sport bike frame or a chopper frame, neither.