Let me jump in. In his Feb 1963 "Duke's Mixture" column, Duke said he was working on the RR 29, it was on schedule, and he wanted to have it out in April 1963. Fox advertised the 29XBB as a "coming" engine in a MAN ad in August 1963. Then in the November Duke's mixture, he said it was shelved.
There was no mention of it in any ads or Mixture columns during 1964. In Feb. 1965, he advertised it again, this time with verbiage reflecting the engine as we know it. Another ad was run in Sept. 1965.
In one of his columns in 1965, Duke mentions the red/maroon flocked paper he is using to dress up the box liners for the Stunt 35, 15RC, and 29X BB. All this led us to attach a 1965 date to this engine for Tim's AMEE and the original ECJ articles.
As a point of interest, if you did out your Sept. 1964 MAN, you'll find an article by Norm Drazy for his Scorcher Proto Speed Ship, with details on how he built a RR BB 29 using some Fox parts and a lot of nice machine work.