42psi is the max load pressure not your everyday running around pressure.
28 front and 30 rear will be absolutely fine.
Just found a reply from Avon tech,
Thank you for the below information.
With regards to the Royal Enfield Classic 500 we recommend 90/90-19 Roadrider with either 110/80V18 or 120/80-
18 Roadrider at the same pressures 28psi front/ 29psi rear.
When riding with pillion or luggage we recommend to increase the pressure by 1-2psi.
Hope this helps.
Many thanks,
Avon Motorcycle Technical