Kingair and the like are both single and 2 pilot
The crew requirements in a flight manual are the minimum crew requirements, you can add more crew as you need/require for the operation. PA31 were equiped for two pilot operations with a co-pilot in mind for the air-taxi/commuter airline business in the USA.
The Metro requires two crew RPT but may be operated single pilot in other operations like freight.
Any other "single pilot" aircraft no co-pilot time loggable.
I was advised by CASA to log co-pilot time as safety pilot for a PPL with a medical condition in a single engine piper. I was monitoring the safety of the flight so therefore part of the operating crew.
The key is if you have a legit reason to act as co-pilot and are assigned for the duty you can log the hours as such. Examples; minimum aircraft crew requirement, company operational requirement, regulation compliance. These days as said before CASA would want the company to have specific procedures for multi crew operation to justify you had a specific role as co-pilot.