Best thing that I have done for mine, was a custom built set of front shocks from Santhuff.

I have a chassis car with ladder bars. I have a solid set of wheelie bars. Ladder bar is in lowest hole. I can go from 4" wheelie to a 4' wheelie by adjusting the extension on the front shocks. About 6 to 7 clicks on extension. Tighter keeps front end down, looser gives bigger wheelies. Too tight and it will spin. I only have 2-1/2" to 2-3/4" of front shock travel. I didn't believe that I could calm my wheelies down by front shock adjustment, when I talked to Santuff. But it worked for me. I also have 51-1/2 % weight on rear wheels, 48-1/2 % on front wheels.