I read an article on radiators a while back and it stated that once you go beyond 2 cores any extra cores lose efficiency because the air flowing through the radiator has already taken on heat from the first cores and is now warm and has been slowed down by impacting those cores. This is why they always place the air conditioning condenser in front of the radiator it becomes hot when the compressor is cycling so it is not hot all the time but when it is it needs maximum air flow to lower the temperature of the refrigerant quickly before it enters the evaporator. The refrigerant needs to enter the evaporator as a liquid not a gas so if it hasn't cooled enough it will still be a gas and the air flow inside the car will not be cold. If the condenser was mounted behind the radiator your air conditioning would not function at all once the radiator reached operating temp and would have reduced efficiency even when cold. If you have a forced induction engine next in line will be the intercooler for the same reasons it needs maximum cooling when required otherwise it will just pass hot air into the engine reducing power and possibly cause detonation. So basically a 26" 2 core radiator will outperform a 22" 5 core radiator even though the smaller thicker radiator holds more coolant because those last 3 cores will not dissipate as much heat as the first 2, the last core will probably do nothing more then bypass hot water. Height and width are far more important then the thickness. Take your 26" 3 core radiator to a specialist and have them remove a tank, clean the cores, pressure and flow test it and I am sure it will work fine.