It depends on the year, which engine code it is, what emission equipment is installed etc. Check the underhood specifications sticker - hopefully it is still there and readable. It should be in front of the radiator somewhere.
Spark plug gap - .034" Point Gap- .021 M/T, .017 A/T Dwell Angle- 24 to 39 M/T. 26 to 31 A/T If the 390 was produced in 1962, the ignition timing was five degrees before top dead center ("BTDC"). If produced in 1963 and equipped with a manual transmission, the ignition timing was five degrees BTDC, and eight degrees BTDC if equipped with the automatic transmission. If produced between 1964 and 1966 and equipped with the manual transmission, the ignition timing was four degrees BTDC, and six degrees if equipped with the automatic transmission. If the 390 was produced in 1967 and not equipped with the Thermactor Exhaust Emission Control System, the ignition timing was 10 degrees BTDC. The ignition timing for all other 390s was six degrees BTDC.
Not sure which motor you have but none offered in the full size vans would have a belt. It would be a timing chain and they will usually last the life of a motor as they are internally lubricated by the engine oil of the motor. I have never heard of a broken timing chain under normal use. Usually they get stretched and can become noisy and/or jump a tooth and cause the motor to loose correct timing and run bad or not start.
What are the advantages of stress interview?
Why the story entitled origin of fair complexion and fair hair?
Ano ang kahulugan ng iskolarling pagpapahayag?
What is a classified data spill or negligent discharge of classified information?
Ano ang papel na ginagampanan ng mga impormasyong ito sa mapa o sa globo?