You also have to get into the rule book as far as motors go. 10 yr old will be in FJB, the top motor is 2 stroke Yamaha KT-100 with small carb and muffler. Briggs Raptor running Methanol, or World Formula with .475 restrictor. Research your poison and drink it down.
My son is Ultra small and light. 50 pounds we have to add 60 pounds of lead to the cadet sized chassis 980mm.
Arrow is a common chassis and parts should not be a problem. 28mm tubes being the best as the young drivers are not strong enough to make a shifter chassis work right.
and 2nd the Ekarting site. I hang out there a lot!!!!!!!!!