I'll be there for this. Mid afternoon launch time means less chance of fog. I saw the last test of this in early 2016. Acceleration is impressive, and expected given their mission.
The first stage looks like a GEM-40 with a skirt welded to its base.
Here's a screen grab from the Orbital-ATK catalogue. The IRBM is basically the same as GBI, with some modifications (like lengthened nozzle on the first stage). The ICBM has a new first stage with the IRBM on top.