Octane levels of gasoline used to be a lot lower when the shop manuals were written for these engines.
With todays higher octane gas, timing needs to be advanced.
Timing should always be as much advanced as possible (leanest setting) before pre-ignition or detonation can do any damage.
This will also give better mileage and improved acceleration.
I always let the engine tell me where it likes ideal timing.
Forget about the flywheel marks and timing lights.
Just keep advancing (turning dizzy counter-clockwise) in small steps until you get slight ping at WOT going up hill in highest gear.
Then just back off until pinging goes away.
This gives ideal timing with any octane gas and at any altitude.
Recurving the distributor and/or vacuum advance is not required with mostly stock street engines, unless you have a race cam and go beyond 3000 rpm a lot.
