What are you going to use the car for? Drag? Circuit? Show? etc.
My recommendation is to find something that has a similar inlet/outlet as the 1JZ, make sure the core size is similar (that is surface area and water capacity) and then find out whether this size radiator will fit in your engine bay. You can get a catalogue of OEM style radiators from your local radiator shop and start measuring 'em up.
I have a feeling the 1JZ is a fairly long motor, so getting the radiator to fit on the front of the car may be difficult. Fit the engine first as these guys have said. You may have to modify the trans tunnel/fire wall and slide the engine back to get everything to fit?
Mounting radiators in the boot is a pain, and you miss out on all that lovely airflow at the front (if you are tracking the car...)
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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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