While we have not been able to test and verify that Wireless Testbench works with the USRP-2974, it should theoretically be possible, since as you note this is effectively an X310.
It looks like this requires connecting your host PC to SFP1 on the USRP-2974 for access to the X310 FPGA, rather than the on-board computer (which is not compatible with Wireless Testbench): https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000001DsV3CAK&l=en-GB
Since you're connecting to Port 0 of the X310, the IP address will be different depending on whether the HG or XG FPGA image is loaded by default. This will also determine the type of host network interface you need (1 Gigabit or 10 Gigabit). It is my understanding that HG is the default image, so will be configured for a 1 Gigabit interface at 192.168.10.2.
Again, we can't guarantee this will work as we have not tested this ourselves but you could connect the NI-2974 (SFP1) to a 1 Gigabit Ethernet interface on your host PC and it should hopefully be usable with Wireless Testbench at the designated IP address.
