It could be MC16 F3. The exhaust port on the standard MC16 was quite narrow, the F3 is wider and much more like the later cylinders. Mine measures approx. 67mm at the widest point measured circumferentially.


Some pictures of mine. I thought I had a stock one to compare against but cant find it!


20190726_150922 by Paul Goat, on Flickr

20190726_150934 by Paul Goat, on Flickr

20190726_150946 by Paul Goat, on Flickr