Tyre pressure

Can't help but wonder if tire manufacturing over 40+ years has changed and perhaps tire pressure specs too? 

I'm 40 psi rear, 36 front.

Thanks for all the advice, I’ve now set them to the information in the handbook (cheers Kawaboy) 36fr 40r and she seems to handle as well as a 40yr old dinosaur can 

Forgot to mention I came to these pressures after trial and error, just riding the bike and noting the handling.