Mike, here is another view; the pin that Denis mentions is definitely the best to access, its worth spending a long suffering time to try and pull it out. Otherwise, the access to the 2 grubs screws is shown here, once removed then yes the shaft can slide forward out of the arm that responds to left/right gear selection...
There should be a boot right outside the shifter box on the shaft, mine evaporated but you must have either grub screws or the "pin" removed to replace. I think I simply unscrewed at the adjustment coupling on the far side of the U-joint to detach from the shift linkage. I've since found replacement u-joints (3 of them somewhere on the shelf, feel free to look, just leave me one for the day I get a chance 
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The then 40-something year old seal finally started seeping after all put together...the shift box should be dry, but suggest getting a replacement seal (it and the grub screws are cheap at Wilkinson, same as the shift boot).
