The engine in Grant's 1981 Century is a 350 cubic inch (5.7 L) "small block" Chevrolet V-8,
converted to electronic ignition.
On 6/6/12, Bud Eiler provided these numbers for
ignition advance on MerCruiser.
I'm unable to find the "basic" advance settings.
(I've seen both 8 and 10 degrees BTDC)