Make that, "the 500
can put out
up to 350 at 8 Ohms". A reasonable watch on the Master Volume can keep the 115 safely within it's rated power handling and avoid any danger. And, if more power is needed, a second 115 puts just
up to 250 watts into each 300 watt speaker.
I usually prefer to stay on the very conservative side of equipment ratings. But I've come around to the idea that, IME, Fender is conservative enough in their ratings that I don't have to use my usual "belt & suspenders" approach. See my recommendation for Rumble 800 speaker(s), for example.