Keep in mind that a large radiator is not always required to keep an engine cool. I'm going to use a stock SEC radiator on my modified LS6 engine, but I'm adding:
1. very high flow dual electric fans. I have a 3400 CFM set from DC Control on my 560SEL, but that company seems to have disappeared. Looks like a Flex-a-lite fan set will be necessary for the FrankenBenz. They make some that go to 4600 cfm.
2. Small oil cooler behind the front bumper
3. medium sized transmission cooler behind the front bumper

Could do more but don't know yet what's needed (if any). The LS6 already has a lower temperature thermostat in it.

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There is a very fine line between "hobby" and "mental illness."
FrankenBenz: '87 560SEC with an '02 cammed LS6 and custom 4L60E.
Bling: '87 560SEC, ported/polished, lowered
Lisa: '87 560SEL, lowered