Hmmm... just took the upper receiver off. The mechbox is black and looks identical to yours, TS, but it's stamped UTG instead of SB.
And yeah, I'll more than likely install the stock spring from my CA M15 in this gun. It was a bit more powerful than the stock TM spring, shooting in the 310-320 range. I fired a few more shots thru my chrony, and I had several that clocked in at over 450 fps. That's just crazy.