Not sure if a tire burning first car is a good idea for your son anyway.
Have him drive the car the way it is for awhile. Let him learn the road.
If more power is what you want,build a 360.
Couldn't agree more. 273's are high RPM screamers like 340's, and very efficient on gas. Did you use 340 valve springs? With your combo it should wind up good but will never have the torque of a 360 let alone a big block. Check your timing and make sure the four barrels are opening all the way when you mash on the pedal.