955 (1300/1550) faceplate on a 953 (1300 only) module explains that discrepancy. Despite my gut reaction that quite a bit of launch fiber would be able to find a home in the module space, (which now appears to be supported by a cursory look at the module) looks like they didn't actually do that, so a launch fiber is the first order of business. Finding a pen that will work in the plotter will be another detail to get to, but not too critical, really.
One moderately annoying "feature" is that when setting the display to show "from A" or "from B" (as opposed to "from origin") it parks A or B in the center of the screen, not the left edge, effectively halving the space available to look at AB things. I had assumed there would be a simple "scroll the display window" method/option, but evidently it's From origin, From A, or From B" - only; or else I'm missing something "obvious."