I guess they are really 2 GTX970's in one system.
Have a look at these systems:
http://www.asteroidsathome.net/boinc/show_host_detail.php?hostid=26048
http://www.asteroidsathome.net/boinc/show_host_detail.php?hostid=100737
http://www.asteroidsathome.net/boinc/show_host_detail.php?hostid=240829
where you have different combinations of GPUs.
Nevertheless and interesting aspect to understand.
Amicable and e@h it seems lists only name for 1 card, unlike asteroids. As tasks at e@h take the same time to finish (+/- 5%) I would be surprised if they are both 970s, as this computer takes either ~1000s or ~3000s to solve a task.
Interesting. All these projects are on different versions of BOINC software, which probablity doesn't help here to obtain the same level of information.