I have an article about MPLS epipe for Nokia 7750 and Cisco 7200 at https://medium.com/@derekcheung/mpls-pseudowire-epipe-interop-nokia-7750-and-cisco-7200-on-gns3-fe398c21f1f0?source=friends_link&sk=ef2d4cb63d37c59b02b22ffbef38a5aa. Although the article uses MPLS as the Underlay network transport, you can change it to GRE by skipping all MPLS configs and on the 7750, modifying the line from “SDP 9 mpls create” to “SDP 9 gre create”. In this way, Nokia 7750 will use GRE as the Underlay network transport. On the Cisco side, you will config a similar GRE Underlay network transport to the 7750. No MPLS is used. Hope this help.