Mark,
I'm glad you asked this question because I needed a reason to go searching for mine which went AWOL...
Like most things with the 'A', the answer isn't so easy. Early Singles - yours, and also mine built Oct-Feb 35/36 - had a 2 piece thrust washer comprising a hard steel ring which fitted partially over the bronze bush flange before fitting the assembly in to the crankcase with a 1 to 2 thou interference fit (heat case first -and ensure oil-hole lines up).
Later singles used a one-piece bush (top of pic) to save all the hassle of the earlier variant. This new bush was made from cast iron and had a thicker top-hat brim at 0.218" (same as the earlier steel piece). Let's face it, I don't really see much input to cause any significant longitudinal thrust from the large idler, so this "production easement" must have seemed more logical. Overall length is 15/16", ID is 0.625", OD is 0.8765". Bob S mentions the later variant in "Ab Initio" - which of course is also widely featured in the imminent
new book - Back to 'A' (plug, plug).
I think you and Greg are both right about idler end-float. It does need some of course, but not much, 4-10 thou max would seem right to me. I don't believe there were ever any figures published for this - but I stand ready to be corrected.
Peter B