The 913 head has lower compression. The engine will produce marginally less HP and torque, compared to an 848, with it installed. Whether or not anyone can tell the difference in performance without the engine being on a dyno is debatable, as some people can be very imaginative when it comes to "feeling" a performance gain.

50-something years ago when I was working on Chris-Craft runabouts powered by the old Graymarine conversion of the flathead six Continental industrial engine, everybody wanted more RPM. Getting the tachometers calibrated to indicate 200 RPM faster than the actual engine speed at full throttle got me the reputation of being the best boat engine tuner on Old Hickory Lake. Everybody bragged about how much faster their boats ran after I worked on them!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!