In this brief section of a teshuva written to Rav Ephraim Greenblatt of Memphis in 1972, Rav Moshe discusses the custom of making a bracha of al mikra megilla on the reading of Kohelet and Shir HaShirim. Doing so follows the view of the Gra, and Rav Moshe discusses whether people who follow this view can make the bracha if they read the relevant Megilla on the last day of Yom Tov instead of on the preferred day of Shabbat.
Rav Moshe first notes that the bracha is only made when the Megilla is read from a scroll written properly (i.e. on klaf, with the proper ink, etc). He then notes that the entire question is based on the fact that the Gra explains the reason for reading on Shabbat as being because Shabbat is a day when people gather together. Rav Moshe notes that Yom Tov is also a day of gathering together (even if not as much as Shabbat), and thus the bracha can be recited by those who have such a custom.