10 ish HP is pretty good out of a 212.... One thing you didn't mention was emulsion tube..... You need that from a gx160 ....
Basic rule of safety with karts....
No cage, no seat belts...
Cage, needs seatbelts. .... You don't want to be strapped in and flip with no cage. It WILL hurt your kid, and possibly worse. If you HAVE a cage , you NEED seatbelts to keep you in, and not get hit or crushed by cage.... Again, serious injuries or worse, CAN and DO happen....
With the kart you have, you should have just got the 13hp ..... You could of bought one easily for what you spent doing upgrades on the 212, unless you're like me and make all my own parts. (It costs me less than $20 to do the mods you did )
Even putting a 13 on it now, you would see and feel a big difference..... Pulling just the governor would put you close to 14-15 HP with only a better breather and exhaust....