Ignition Switch Type B-6 Dual Engine WWII

This is a WWII-era Ignition Switch Assembly, US Army Air Force Type B-6, for a dual engine aircraft, made by Bendix-Scintilla for Delco Aviation, part number 10-30910-1.  The B-6 ignition switch has two switches, one each for the left and right engine, and a master switch in the center. The master switch is switched by pulling (ignition off) or depressing (ignition on) the center post, intending to be able to kill both engines simultaneously. The knob on this example is missing.

We have observed the dual ignition switch with a push/pull master switch in manuals of early versions of the C-47 Skytrain transport.  While the B-6 may have been used in some versions of dual engine aircraft such as fighters P-38 or P-61, and bombers B-25 or B-26, all documentation we've seen on these aircraft illustrate the type B-5 ignition switch, where the master switch is a flat toggle instead of a push/pull switch as designed in this B-6.  

It is clearly experienced but otherwise in reasonable condition for its age. The engine switches turn and the master switch pushes/pulls stiffly even without the knob.  Measures ~4 inches triangularly by ~2 inches deep.