I can say with confidence that you won't be able to re-use any of the components in the Slow Stick on the much larger and heavier Piece O' Cake. A plane of a certain size and weight requires a certain amount of power to fly. The amount of power is proportional to the plane's size and weight.

Since power is derived from Volts and Amps, a bigger plane needs more Volts and Amps. Your Slow Stick flies on about 8.4 Volts and 8 Amps, has a wingspan of about 36", and weighs about 12 ounces. The Piece O' Cake has a 72" wingspan, and weighs about 24 ounces. It's going to need about twice as much power because it weighs about twice as much.

You can double power by doubling Volts or Amps, and keeping the other the same, but it's easier to increase both.

The Piece O' Cake should do well on 8-10 cells with a Speed 400 or Speed 480 motor.