Thanks everone for replying.
Just went to half price book shop and picked up a copy of Haynes. I expect I will be using it quite a lot now.
I also think it is a retaining pin. Have not found it in the book yet. Perhaps get a chance to look later. The tilt lever does not have a nut that I can see. It does have two flat sides on the stem so perhaps the whole thing turns.
I think I will need to see if Autozone carries a retaining pin before I go much further. I'd hate to have it all in bits then need to walk five miles to Autozone.