Odd Overprint On "R155"

All,

Found this while paging through my album. Completely forgot I had it. Had it hinged off to the side of the page.

Any opinions on what it is or why it exists?

Appears to have a postal canx. Question is why would anyone bother to try and create an R155 from a postally used stamp? The "1879" date, if genuine, is 19 years too early for the 1898 series. In a stretch, it could also be an Aug 1899 canx (/8/9). I have seen several battleship canx that only use the last digit of the year in their canx. I am grasping at straws here - don't think this is the case with this stamp.

Still seems like a lot of effort to create a cheapo stamp!

With that date I would lean towards bogus philatelic contrivance rather than any kind of provisional overprint.