Austrian 65 engine work/pipe?

Looking for some recommendations from mini dads who have had motor work done to their kids 65’s..

My son is getting fast, especially for riding for less than 2years and we are going to start racing some ama races this year. Have just been doing some of the local SoCal series up until now..His bike has been stock aside from jetting, vforce reeds and a husky hard parts silencer but I recently got him the Bud racing spring conversion for his forks which made a huge difference for him but now we arnt eligible for the stock class..

He’s beaten plenty of kids on trick bikes with his stocker but if we are going to spend the time and $ to try to race mammoth he probably shouldn’t be at a disadvantage out of the gate. Who have you guys used for cyl porting and what pipe have you guys had good results with? He isn’t a rev’er, he’s pretty good about carrying his momentum and I’ve noticed he rides a gear higher than the other kids which I haven’t tried to discourage. He’s a little bit off the two or three fastest kids but he can beat the rest and he gets better every time he’s on the track. We just do it for fun and have no delusions of him being pro but I also know what it’s like to ride a total pos when you are a kid and everyone else has a good bike and I told myself I wouldn’t do that to my kid..
 

We don’t have allot of money and I make allot of sacrifices to keep a fresh piston, clutch and tires on his bike so don’t want to waste $ on a pipe if the difference over the stock one is negligible..

Thanks for the help