Man, most of these engine don't open up until 5,000 RPM. A Mikuni just for 4,500 RPM? Talk about a waste of money on a thin wallet. If you're not going over 4,500 RPM just stick wit ha bone stock Ruxing and rejet it, man. That's where you'll save money.
8 deg timing key just for 4500 RPM? Na, man. Better ways to spend you money. better combos are available at this RPM range than advanced timing, Mikuni carbs, tuned exhaust, 280 lift cams just for 4,500 RPM. It's just not worth your time, man. Of course you can do whatever you like, but most everyone here is pointing you in a different direction.
Unless you're turbocharging getting tons of torque on a low displacement motor is just a bad idea. A happier balance of RPM, carburetor, cam and compression will give you a better performing engine. I don't build race engines either. Hate to burst bubbles, but if reliability is the main goal run a bone stock motor and never change it: maybe stage 1 to make the motor easier to work on.
If you just bumped it to > 5,000 to < 6,000 RPM, rejet carb, good old MOD2 or the 265 cs dyno grind, maybe 9 to 9.5:1 compression, you'll have a nice little engine that won;t win any races, but will get you out on the dirt and having fun without too much wrenching..