You'll be fine. The safety issues aren't a worry in such a big vehicle like that. If they were, you can bet the bus company would be held to enforce carseat laws like everyone else, especially with lawsuits and liability being what they are these days. If you have concern, wear your baby in a sling or Ergobaby carrier, or something to keep them close during the ride. That way they are a little more restrained than on your lap.
Like the previous poster said, big giant "greyhound bus" luxury motorcoach - with no seat belts or restraint devices in the big cushy seats. At 8 months, I'm guessing she's almost out of her bucket seat, so you won't need to bring that along for convenience like you would for a 3 month old.