Dougie, interesting picture and thoughts about the saddle tank covers.
I see 3 covers in thepicture though, not just 2. There's a 3rd cover at the right, just at the top of the white streak that might be some discolouration due to diesel fuel leaking out and making some of the paint flake off. It's oriented the same way as the middle cover and has the 3 dots going the same way as the middle cover.
And yes, the sahpe of those two covers looks different than the cover at the left. They seem rounder, not as much of a flattened ellipse.
As for the 3 dots, they seem strange but I'd guess they have something to do with how the cover is fastened to the hull plating, or how the fastening is unlocked. Perhaps there's a tool, like an allen key sort of thing, that fits into a socket in the dot and lets them turn? And when they're turned, they turn a lever inside that releases catches that hold the cover down? Sort of like the wheel on top of the main hatch of the conning tower, but not in place all the time for hydrodynamic reasons?
Perhaps 3 holes as the ones at either side something that the handle locks into for mechanical advantage while the centre one is where the tool sockets into?
It also looks for sure that these covers are slightly raised from the plating on the saddle tanks, as if they fit over a slightly smaller hole rather than get inset into a hole to be smooth on the outside.
