Running engine with only timing belt

My dad and I just tore apart our 1997 Plymouth Voyager's engine and rebuilt it, but now we have an oil leak we can't track down. He'd like to run the engine without any belts on it except for the timing belt, but isn't sure that that's possible - he thinks we might need to make sure the generator is hooked up to power certain components, but it's also possible the battery can power everything for a couple minutes.

Long story short - is the timing belt the only critical belt for the operation of the engine? We'd like to take as much off the engine as possible to get a good look at what's going on in there.