I've been running 4 degrees BTDC, with manifold vacuum connected to vacuum advance to add additional timing at light throttle cruising.
This puts me at odds with everyone else who runs ported vacuum, because it makes no sense to me to have no advance at idle, followed by advance at part throttle, then down to no advance at full throttle. With manifold vacuum I have full advance at idle and light throttle, which tapers off as the throttle is opened.
My HEI has centrifugal advance that starts at 1300 RPM and adds a total of 13 crankshaft degrees by 2800 RPM; the vacuum advance adds 19 crankshaft degrees when the throttle is closed. My plugs are set to 0.060" gap, which isn't easy.
Marty