Thanks Dennis and Steve. I have the AOE instructions, Steve. That article adds more useful information, thanks Dennis. With a bit more research, I know where to look for the other screws now - at 90deg to the first screws. Must be under a bit of the rubber that was glued down. I'll carefully look under there tomorrow. I'm not beaten yet!
Mind you, some of the reading suggests that collimation by eye is a poor substitute for the use of proper alignment tools.
I also read a great tip for collimating at night, on a star - defocus one side with the diopter adjustment and then you'll have a sharp star image and a fuzzy ball. That doesn't fool the eyes and you can adjust to place the sharp image centred in the fuzzy ball. Sounds like a good approach.