All the examples that I have seen and believe to be of good provenance have the spring between the drawbar and crossbar. There is no real other way to install the 1120-6 trailing truck. The spring is installed at the factory, and the the service documents depicts it as your part is shown:
Here is the 1130-20 that @Chuck Sartor mentioned. It is derived from the 2034 locomotive as noted. The motor is of a differing setup and am unsure if the 1130-20 will mount where the 1120-6 is without modification.