26 Two and Six Half a crown, Half a dollar in slang, in old money. Money was more fun in the old days we had florins, tanners and because it was not decimalised people had to learn more than their 10x table to deal with it.
27 is a perfect cube - 3 to the power of 3 Or if you want something more obsure - it's the highest level of knowledge in rupaloke (Buddhism).
rep I saw on your profile Andy that you mentioned Greenditch Ave are the Blocks of Flats still there at the end and is the grassy area by the stream still called the dump as it was back in the late 50 early 60's? and I seem to remember the school was Whitehouse Junior school or at least it was when I lived there and went to that school.