Dual Radiators: series or parallel?

[Procharmo]

I will be running a gear drive twin F1C Procharged SBC 406 street car. I have two 12 x12x2 aluminium radiators with 11" fans.
They have -12AN fittings, there is also a CSR electric water pump with heater outlet.
Which will be more efficient, the radiators connected one after the other in series. Or using a pair of Magnafuel -12AN y-blocks feeding them in parallel?



I need to be able to idle in central London traffic, burnout, then idle again, for hours on end in summer heat!!!!