Hi Dan O'Meara:
From some notes I've uncovered here in my study tonight, I can tell you that the recordings used on that McAdams page are made from a cassette tape recording which was found in the Minneapolis Public Library many years ago by researcher Dave Dix. What I can tell you about it is that it almost certainly originated from a tape recording which originated from within the Dallas PD pre-1967. The tape recording was given to author Judy Bonner, who was at the time writing her book, “Investigation Of A Homicide”. In June 1969, Ms. Bonner’s tape was given to, or copied for, Dallas researcher Mary Ferrell, from whose tape most of those in the hands of early researchers until the early 1980's originated. Interestingly, examination of this version of the tape shows that it contains identical splice sounds (caused almost certainly, I believe, by shorter individual tapes being joined together in making the Bonner tape) to those on the recording found by Dave Dix - in other words, the Bonner/Ferrell tape unquestionably came from the same source as the one found by Dave Dix. As for the transcript, I know that Ms. Bonner included a transcript of the tape in her book, and the Channel 1 version attributed to Russ Shearer on the McAdams site appears to be a stripped-down version of the one in Judy Bonner's book. It is not, therefore, a verbatim transcript at all. The transcript in Ms. Bonner's book does not make any reference to the splices you mention, but the same splices are referenced in a different transcript of (presumably) the same recording which was subsequently made by Dallas researcher Arch Kimbrough around 1969.
You can therefore see from the foregoing just some of the difficulties that have been created over the years by transcripts - not all of which are verbatim - made by different people of what purports to be "the DPD radio recordings", but which are in fact copies - and usually copies that are many times removed - from the original Channel 1 dictabelt recordings. This cannot answer all of your questions, I'm afraid, but I hope it does explain why some very strange timing discrepancies can and do arise.
Sorry I cannot add much further at this time, but a detailed study of the recordings and transcripts is something to which I devoted a lot of time some years ago as I recovered from major heart surgery, but I'm essentially semi-retired at least from the research field now, and most of my old and rarely-accessed files are boxed up and stored off-site.
Chris.