Do you have details on how you are planning to do this? I've looked into building and customizing radiator cores, but by the time you consider costs for doing so, you end up paying much more than just buying a normal watercooling radiator. Even heater cores are priced in the range of lower priced radiators, plus with heater cores, you still have to braze or solder on fittings for use.
But, being one that has gone the heater core route before (1986 Chevette heater core; still have it), I'm always interested in DIY watercooling. Keep us updated on your work.