ear approximation, I just play this twice with some creative trills or bending:
[ Tab from: http://www.guitartabs.cc/tabs/w/willie_nelson/always_on_my_mind_tab.html ]
e--------------------------------------------------------------------------|
b----7-8-10-8-7-7----------------------------------------------------------|
g-----------------9h11p9~--7-9-11-9-7--------------------------------------|
d-------------------------------------11-9--7-7h9-7------------------------|
a--------------------------------------------------------------------------|
e--------------------------------------------------------------------------
|