Suspect you are right, and as I recall the details they fit the "proto-Celt" timing. A lot of early European (and ???) history fits the proto-Celts.
All the earliest skeletons/mummies found from the Black Sea into the Gobi desert were Caucasian. It was only much later that the Asian skeletons (mixed) began to appear (in that region) and even later 'full bloodied' Asian skeletons began to appear.
"Although traffic had been moving through Central Asia for millennia, whether across the steppe or from oasis to oasis along the edges of its deserts, it was Zhang Qian (d. 114BC)who brought Western Regions to the attention of the Han government."
It was the Han government that finally (after many failed attempts) conquered the Caucasian territories all the way back to Bactria. Many fled the Han armies all the way back to the Caspian and Black Seas. (These folks ought to begin to turn up in some of your studies)