Hell of a buck!
Allowing 100" on his frame I am coming up with 58-60" up top.
I suspect being a panhandle deer he may be heavier on the frame so my guess would be 160-164"
Using a similar, if not the same, method, I got to 157" assuming 6 inch ears. I've hunted the Panhandle for over 20 years (after hunting Mason jackrabbits for the previous 20+), and, from my observation, the ear lengths regardless of body mass are pretty much the same. Hope you'll let us know once you take him!