Actually the 40 series opposed twin started out as a 12.5 hp. It grew to a 14 hp then finally a 16 hp. At the end of the run of 42 and 46 opposed twins several different stickers were stuck on the remaining engines, lower than their original rating and generally ending in .5. All the other remaining flat head stock was done similar.
While Illinois is a pro and his settings will work, actual spec is .003"- .005" for the Intake and .005"- .007" for the exhaust. I go for the min. on the Intake for compression release reasons.
I can send you detailed instructions on setting the valves AND a Service Manual IF you like. Address below, put in proper format and remind me engine model number and what you want.
Walt Conner
wconner5 at frontier dot com