Ac generator from ac motor?

Me and a friend of work with large scale trains (1.5" scale, 7.5" gauge), and we are in the process of making a maintenance of way car. We want to know if we would want to use an alternator running through a DC to AC inverter for power or if we can just run an AC motor and have that as the generator. We will be using a 3.5 hp Briggs & Stratton engine for running the generator.