The Cummins 8.3 is a great engine. It is a sleeved engine and as long as the weight of the coach is within the 1HP/100LBS range it should perform well.
I too would insist on seeing some maintenance records and checking the SCA levels as well as making sure they have been maintained over its life. Letting that go can create issues liner pitting and potentially end up with coolant getting into the liners over the course of its life.
Mike.