I would stick to the PA-44 and PA-34. Their systems are fairly similar. If you study one, you will know 70% of the other. Remember the main difference is the seneca is approved for icing, is turbocharged, and has air conditioning so there are a few more systems to explain. Also the fuel system has some differences as well. Then remember the what would you do questions - if this failed and then that failed and there are no airports, it's a hurricane and complete sandstorm, and one of your passsengers is having a heartattack and you have 15 minutes of fuel left type questions!!