The top of that tom mount looks to be round and with three holes. Never seen that before. Maybe this was designed for the apocryphal three tom set-up pictured on drum catalogue covers but never actually seen in the wild.Not loving the colour - looks like mid-80s Prince exploded all over it but for $750, how wrong can you go? I played a kit like this for most of my twenties. A thing of awe.
You guessed it. That's exactly what that round part is. There are three holes designed to mount three tom arms to it. I have one in my parts drawer.