If you are referring to a 420 116.xxx engine then the plug gap should be .8mm or .032 in. The timing is handled by the EZL ignition unit and the crank shaft position sensor at the left rear of the engine. It is not adjustable. There is a setting for the distributor but it is done by setting the engine to TDC and then setting the distributor so the rotor points to a mark on the dist housing. You can use a timing light to check the EZL function for advance but I don't think I have ever seen any specs.

Paul

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84 500 SEL (307,xxx miles)