Hello Gubfan1962
I bought this product 2-3 years ago for my Lifestyle 500 system at the time. I don't know right now which bracket connection the Invisible 300 has. But I had several adapter options for different boxes from Bose. I'm pretty sure these are compatible and everything is included to hang them.
I'm not sure, but I wasn't sure at the time either and bought them on the off chance and everything was tip-top and surprisingly easy to hang up.
Regards