APS Engine

The Smithsonian displays a lunar module Ascent Propulsion System engine.

This particular engine differs from other APS engines I've seen: The propellant lines on the forward end of the engine seem different, there are more components mounted around the periphery of the forward end of the engine, and the nozzle is covered in some sort of black tape (rather than either the natural gold color of the windings or painted white); even the shape of the "lip" at the exit plane of the thrust chamber seems differently-shaped.

The Smithsonian's Collections Database entry for this engine states that this particular engine was tested at White Sands in 1964 and later installed in an LTA for thermal tests at Grumman. So, I don't know if this particular engine retains some additional components which are typical of an installed engine (and which are not present on any of the other engine currently on display) or if these additional components are left-overs from its testing regime.