I came across a data sheet that recommends from the factory certain tire pressures using Michelin tires. These are only a place to start as this is dated 28/2/1964.
Speed up to 100 mph Front- 22.7 Rear- 25.6
Over 100 mph in short peaks Front- 25.6 Rear- 29.8
Continuous Highway Front- 27 Rear- 32.6
On track Front – 32.6 Rear- 36.9