Wait! Hold up!
You need a decoder with the plungers? I think I have one that I'll happily make yours for a song.
I actually got that decoder running. It does indeed have an F2 function and I was able to wire up the marker lights correctly.
As luck would have it, I have ANOTHER early IM F7 that needs a decoder, so I'll gladly take yours off your hands. What do you want for it?