I'd suggest using a delay-flash timing light and setting the total timing to 35-36 degrees at 2500 RPM with the vacuum advance disconnected. Once any towing load at all goes on the engine, the vacuum advance will be virtually nonexistent, and most initial + centrifugal advance settings at cruise speed work best at around 36 degrees. One degree over-advanced robs as much power as a 5 degree timing retard (proved under load on my dyno repeatedly) so an error on the low side of timing advance is better.
Jerry

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