Thanks to TMA, I was able to track down the three other sites on Stanton Moor (North, Central and South). It took me a while to find the “T56” marker as it was quite overgrown with heather. Not sure whether its allowed, but I did take out my trusty Swiss Army knife and cleared back the heather from this marker in the hope that it will make it easier to identify for others (see photos I just posted).
After visiting this area quite a few times now, I am amazed that I had walked past it without realizing.