Jeff,

I own several of the Trix UP 'ACR' 40ft boxcars, and the springs are associated with the Trix couplers.  You can remove the couplers, draft gear boxes and the springs with no danger to the operation of the car.  I think I had to fill a hole in the floor with some sheet styrene before attaching Kadee couplers and draft gear, but that was all in a day's work to get the cars equipped for layout operation.  I would check my installations of the Kadees, but all of those boxcars are in storage elsewhere.

Others may chime in with their solutions.

Todd Sullivan