Try really hard to get into the fixed base sim for a few hours. The instrumentation is not a big deal, the same information is there in both layouts although on your first flight in the aircraft a lot of the EFIS info will be surplus to your requirements.
If as a low time guy applying for a right seat you can show that you fly accurately, sensibly, economically and look after their aircraft you have done more than enough. Time in the fixed base sim will just make you that bit more comfortable with the speeds, limitations and how it handles, close the throttles on a seneca and not much happens, do it on a twin turboprop and you may be surprised how fast you come down, slow down or both.
Am sure you do this already but look after their engines, you say its a small operator so those two engines are a big deal. Be smooth with them, don't leave them at max power when it is not required, assume you will be light so it wont be long after take off that you will be reducing power. Know the limitations, engine temps for max start, max continuous etc, know the weights and know limiting speeds. Those are the minimum limits you should know, anything else is a bonus but dont get carried away with oil temp limits etc, that's what the green bands and red lines are for.
Good luck.