Use standard ethylene glycol antifreeze mixed with deionised water (or soft tap water) at a ratio of one-part antifreeze to two parts water. It would do no harm to flush the system a few times with plain water to remove sediment. Fill it up, run the engine until hot then drain the water. Allow it to cool fully before refilling.
Oil capacity: 9 1/2 pints (5.25 litres) of 20W/50 mineral oil. Make sure it has an API rating as a mark of quality. Also check the levels in the gearbox, final drive, power steering and carburettor dashpots. Track down a workshop manual for further servicing data – or consult the P6B Service Guide in the July 2013 issue of Practical Classics.