Indeed! Black Cortex is the finish (one of my personal favorites)...and your set seems very well kept.
Can you check the numbers on the badges and list them? That would help me to determine whether or not all the drums were initially sold together as a complete kit.
All the shells are the famous 3-ply shells -a good thing.
The fact that some are clear and some are Granitone is unusual for this particular configuration due to the fact that the interiors were visible and, thus, likely would have been sold with a uniform interior finish. But, then again, Ludwig was known for putting out many matched double-headed kits with different interior finishes, so that's not necessarily pertinent.
Since your drums appear to be in good shape, I would put my estimate at the higher end of the scale for such a kit...which isn't really meant to suggest an abnormally high value...but one that reflects the current state of collectibility for single-headed concert tom drums.
The value is in those bass drums. They are "adaptable" to other configurations outside of the OctaPlus. Also, the big floor tom is collectible. The value is also in it's completeness -IF it turns out to be a matched kit (based upon the badge number sequences) as a representation of one of Ludwig's most ostentatious configurations.
I am looking at the 2 bass drums being worth about 300-350 each..the 18" floor tom another 300. The smallest toms (the 6 and 8) are probably worth the most out of all the single-headed drums...maybe another 200. The other single-headed toms are probably worth about 50 bucks apiece. So, individually, the drums are worth about 1,500 or so...
...BUT...the completeness factor could add another 500-1000. The right collector...the Ludwig collector who wants one of every configuration...would love to have such a nice representation of the OctaPlus. So, I'm going to go out on a limb and say that I think your OctaPlus is worth about 2,200...and maybe even a bit more by adding a matching Supra snare.
I wish I had the room for them in my collection!
The gong may be semi-valuable, too...but I don't know the brand or how to estimate a value for it.