The oil capacity will have nothing to do with the actual piston swept area, the displacement. Post the serial number off the engine here and we'll see what can be discerned.

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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