The BJ4 was made by Jconcepts & then they sold the design to Associated & Associated made the B44 based on the BJ4 layout.
The Atomic S4 was a slim tub chassis conversion for the BJ4
The Atomic S44 was a slim tub chassis conversion for the B44 as used by Chris Doughty to win the EPR National in 2009
Hope this helps.
Marc