Overinking of the red overprint is indicated by streaks of lines and a
dot. Also, the stamps at right in this vertical block of six have
larger paper sizes than the ones at left due to boardwalk margins at
right side.
90-sentimo Philatelic Week overprint of 1979 on ₱1.60 Felipe Agoncillo stamp of 1976.
A railway post office cancel of the Manila-Legaspi line.
It
says SOUTH so this must have been on mail from Manila to Legaspi, or a
way station in between. (If NORTH then it would have been on the train
from Legaspi to Manila.)