Those letters are dated 26/5/74
I suppose they could have been published, within reason anytime from then!
He got a letter back saying that the could not print the photos he sent in as they did not have the means and that they had kept his letter for use in a future issue.
One thing I know for sure, it was definately published at some point because he gets a postcard (bottom of scan 2) from someone who had read his letter and says about her 66 bug "I wouldnt part with her for the best Rolls going!"