Looks like my browser was messing up. Kept sending me to the main manual page.
And from the manual:
Use any good grade automotive regular or premium gasoline with a minimum average octane rating of 88* (93 research) in your PCM engine.
An 86* average octane (90 research) gasoline may be used if the gasoline described above is not available; however, the ignition timing MUST BE retarded 41 to prevent harmful detonation.
*New U.S. Regulation requires posting average of research and motor octane.
PCM reserves the right to refuse warranty on parts which are damaged -when using improper gasolines.
It clearly says use any regular automotive fuel and can have an average of 86 octane OR premium 88. There is no doubt that 87 is just fine for that engine.
Gone, out doing soft recreational past time with overpowered boat!