You can call the GetLeftPort and/or the GetRightPort methods to get the port(s) corresponding to a particular item in the GoMultiTextNode. For generality, such objects might not exist, and might not be instances of GoPort, so you will need to check and cast appropriately.
GoMultiTextNode mtn1 = …
GoMultiTextNode mtn2 = …
GoPort p1 = mtn1.GetRightPort(3) as GoPort;
GoPort p2 = mtn2.GetLeftPort(2) as GoPort;
GoLink link = new GoLink();
link.FromPort = p1;
link.ToPort = p2;