hi, sorry for delay.
anyway, the new Polini 210 alluminium (not cast iron!!) it's probably the best px200 gt. lot of torque and rpm. the cast iron model it's not a good choise lot of problem with that.
for a first step, gt+ crank+ 28carb it's ok. you also need to change the gear ratio, maybe a polini/malossi 23/64 it's the best choise.