Ideal amount of oil for a /6

My 1965 owner's manual calls for 4.5 quarts (imperial) with a new filter, which translates to 5.4 quarts (US).

Once it's broken it, I would use a low viscosity heavy duty engine oil like 10W-30. We can get 0W-30 in Canada but I don't think this grade is readily available in the USA. One of the guys on slantsix.org has been using M1 0W-30 AFE and has been quite pleased with it (see Oil Question).

ACCCC Engine Oil Article