I didn't know so much could be written about Spanish-Philippine postal history until I read the book Postal History of the Spanish Philippines 1565-1898 by Don Peterson and Geoffrey Lewis.
This hardbound book has a copyright year of 2000.
It is illustrated in black and white.
Bought my copy by mail from Don Peterson in the US.
Came with a dust cover.
Unfortunately, pages 159-174 are upside down!