I'm no expert, but from what I understand long vs short is how much it protrudes into the frame. Longer being just like longer intake runners, which has been shown to give more torque but less high RPM hp.
Obviously 3D printing is not BRAND new, but it's still fairly new. Muzzy's is now gone. I assume BEAR is still just rocking what he knows. Perhaps guys like Brocks are maybe looking into 3D stuff (probably not for the 12R though, these bikes are dinosaurs). One thing to consider, and I know it keeps getting better and better, is the stregth of the printed material. How is that plastic going to hold up vs aluminum? When we talk about something that needs to potentially last a LONG time. There is no doubt aluminum pieces will most likely outlive the bike. Can you say the same about printed bits? Sun, rain, vibrations, flex, etc.... I could see cracked pieces very likely.
I personally would be very interested in hear how your project turns out. If nothing else, it'll be a cool piece on your desk.