I finally acquired a copy of TSR's 1977 Legions of the Petal Throne. It is a wargame based on the peculiarities of Tekumel. It was written by none other than Dave Sutherland! Illustrations are by Dave Sutherland, Dave Trampier, Tom Wham (just line drawings of miniature terrain in Wham's case), and M. A. R. Barker. Let me tell you, Sutherland was born to draw Tekumel stuff. I think it is his finest art. One of these days I'll see if I can scan some of the better pieces and share them here.
I also own this, but it appears that on page 25 my copy is missing the Medium ranges from the 'Missile Weapons and Ranges Chart'. Geoffrey, does your copy happen to have those ranges printed, or was this intentional?