In the old Yerushalmi Torah reading tradition (the triennial cycle), when special days fell on Shabbat, the regular Shabbat reading was interrupted: the Shabbat morning reading consists only of the reading for Rosh Hodesh, Hanukkah, etc. See, for example, Yerushalmi Megillah 3:5 (= Vilna 25b; for my additions, see Korban HaEdah ad loc, and R. Goren and R. Ginzberg on the parallel yBrachot 4:1):
ירמיה ספרא שאל לרב ירמיה ר"ח שחל להיות בשבת במה קורין א"ל קורין בר"ח א"ר חלבו קומי ר' אימי מתניתא אמרה כן לכל מפסיקין לראשי חדשים לחנוכה ולפורים
Yirmiyah the Sofer asked R. Yirmiyah: On Shabbat Rosh Hodesh, what do we read [in the main Torah reading]? He replied: [We read] about Rosh Hodesh. R. Helbo said before R. Immi: The Mishnah agrees: "They interrupt [the regular order] for anything: for Rosh Hodesh, for Hanukkah, for Purim, for fasts, for Ma'amadot, and for Yom HaKippurim." (mishnah Megillah 3:4).
Additionally, the practice in Tannaitic times was that only the first Torah reader said a pre-bracha and that only the last reader said a post-bracha (see Megillah 4:1). However, some specific portions of Torah reading require their own brachot (perhaps not the same ones as the brachot mentioned above). For example, in Yerushalmi Megillah 3:7 (= Vilna 26b, also Soferim 12:4, p. 225 ed. Higer), we read the following:
ר' יוסה בי רבי בון תמנתי פסוקיא אחריא דמשנה תורה טעונין ברכה לפניהן ולאחריהן בלא כך אין הפותח והחותם בתורה מברך לפניה ולאחריה לכן צריכה ראש חודש שחל להיות בשבת
R. Yose ben R. Bun [said]: the last eight verses of Deuteronomy require a bracha before and after. Without this [statement], doesn't the first and last reader of Torah make a bracha before and after? But this [statement] is necessary for Rosh Hodesh that falls on Shabbat.
I understand the question on R. Yose ben R. Bun to be asking about the necessity to state the requirement for a post-bracha (since the person reading these verses will necessarily be the last reader, and so automatically will require a post-bracha; see the Korban HaEdah). However, I don't understand the resolution of this gemara. Some explanations I've read:
Some commentaries explain that the case is reading the Rosh Hodesh reading as aliyah 7 after reading the last eight verses of the Torah in aliyah 6. One needs to make an after-bracha after aliyah 6, even though this isn't the last reader. But this is unsatisfactory, since it's in contradiction to (the way I understand) the triennial cycle (R. Kanievsky explains this way, and concludes that this gemara disagrees with the rest of the Yerushalmi). This explanation would be more satisfactory if there were other sections of the Yerushalmi that also taught this way.
Heinrich Guggenheimer explains that the Rosh Hodesh reading (Numbers 28:11-15) had to be read seven times on Shabbat (explaining mishnah Megillah 3:4 as we have above, and since having 5 verses, it can't be split). He says: "Since starting and finishing readers read the same text, it remains questionable why they should differ in their benedictions". It isn't clear to me what Guggenheimer is saying: is his conclusion that in fact all seven readers say both brachot, since they all read the same thing? Or that in spite of it being "questionable", still only the first and last reader say one bracha each? And how does this relate to the original question about the last eight verses of the Torah?
Can anyone explain this gemara, either with a separate explanation than the above two, or explaining one/both of the above explanations in a more satisfactory way?