A little more research led me to the name of the armored train featured in the last couple of photos I posted.
https://en.wikipedia.org/wiki/Krajina_Express
And another pic for good measure.
From the various photos I've found- all of which appear to be of the same armored train- it looks like this bad-boy was armed with
at least:
A 76mm AT gun (in an M-18 Hellcat turret)
Dual aerial rocket launchers
A Bofors-type 40mm AA gun
An Browning M2HB HMG
A quad-mounted HMG of some sort (possibly a ZPU-4)
Two AT-3 Sagger ATGMs