This probably isn't the best place to inquire about mechanicals on a Mercedes school bus. To the best of my knowledge there has never been one of those beasts in the US. Cowlitzcoach would know. And since you haven't posted any pictures I don't think there is such a thing.
I'm not sure there are even any Kiwi's on this forum, not recently anyway. There are some on some of the other bus forums. Bus Grease Monkey has at least one.
We are however, quite prolific with free advice on a staggering range of other topics
. Remember, things we can get away with doing here are not allowed by the gov'ment down there. For the most part, if it's an RV we can do pretty much anything we want.
Do your research.