Seems like a lot of expense and R&D for such a limited HP engine to me, I've never run a governor on a 3hp briggs due to the way I set up the throttles but never made enough revs to float the valves. I maybe see justification for the rods on the little predators but as you found out first hand the flywheel seems to be the big concern on the baby clone engines. Billet rods and flywheels just go together when we talk excessive revs on any small engine really. Also I wonder if the minibikes you are running are just too small for a good old briggs fiver or you are just intent on making the small engines not grenade under excessive loads. As far as the 2.8 lifan it seems an exercise in futility given all the other problems they are plagued with. I've sold parts off them to aid in a member getting one running for a kid, even gave a few parts and one complete 2.8 away. Too light to use as boat anchors so I figured parting em out was best plus it generated income. I've never seen a well performing 2.8 but that don't mean there have never been any. I watched my kids kill three after 6 hour days of riding normally and two were new. My Daughter now runs a 3hp briggs ungoverned on her DB and it's on it's fourth season of hard riding so I'm all for trying to build a hot little 3hp myself.
I found a small generator on big trash day on the side of the road powered by a 3.5hp briggs with weird intake/carb and weirder muffler, I opened it up and found that it had an aluminum flywheel on the horizontal shaft mill so I kept it. I want to get a camshaft custom ground for more lift and duration and cut the eyebrows and port the head. I have a nice OHV 5.5 briggs carb and 5hp briggs bowl type carb composite intake and will make as big a pipe as possible. My goal is more RPMs and HP with the less rotating mass the flywheel would provide. I also plan stiffer valve springs if I can source some. My reason is that I have a Stellar which is limited in engine height, I have a 1970 3hp with tons of compression that is a candidate but I have several 3.5hp mills I could use which flow better already. I will build a better 3-3.5hp briggs and I plan for it to rev past 5k wit the mods I am looking into, a rod with a less brittle dipper would be smart to use though. I'll watch what happens with your setup and decide which direction to go with mine. At least someone is trying to improve the small clone performance.