SIC QUALIFICATIONS part 91 usa Challenger

[737WJD]

I'm a current 737 captain
A friend wants me to SIC on a part 91 flight

What other things do I need to accomplish before the flight other than being familiar with the airplane systems

Confused after reading part 91 Do I need 3 T/o in that airplane or any airplane

Thanks for help

[galaxy flyer]

FAR 61.55 paragraph b says it all. Must be in type, must include some OEI work, can be in approved sim.

GF