If he wants you to do some approaches and fly the airplane ask if you can sit in for a couple hours and learn where all the switches are. I've never touched a 90 but the 200 I used to fly was very flow friendly. Meaning if you were landing you flipped one switch then the next switch and so on in a nice logical flow each time. I had 22 hours Seminole time when I went to Flight Safety on the 200 and it was tough but not impossible to fly single pilot but I had the luxury of having been able to sit in the airplane prior to getting hosed in the sim.
Congrats on the opportunity to fly a Beech, the BE20 and A36 are two of the finest flying aircraft I've ever flown.