Looking for a little help from you Slingerland experts in identifying a double tom mount I recently found. This looks like an early version of a Slingerland set-o-matic tom mount. The pieces that the ball fit into and the plates that mount on the toms are cast aluminum. The receiving hole in the tom plate is the familiar "D" shape that I have seen before on these mounts. The thing that is confusing me is that the post for the arm that goes into the bass drum mount is round and not "D" shaped. I don't have the plate that mounts on the bass drum and there is no Slingerland name anywhere on the arm or tom plates. Is this an original Slingerland part?
BTW - The inside of the tom mount has the part number 150-6 stamped into the metal. Seems like the correct part number for a Slingerland set-o-matic?
Thanks in advance for your help!