The following is from the Eaton Marine Interceptor manual, which pertains to the 352, 390, and 427 Ford based marine engines.
From my Eaton Marine Interceptor Manual
IMPORTANT NOTE: you 427 Chris Craft guys will notice the valve lash setting for the Interceptor version of the Ford 427 with 300-hp is different than the Chris Craft recommended setting. I have no explanation for this, but I suspect the 300-hp 427 used the exact same camshaft for the Interceptor and Chris Craft versions of this motor. Now, since Interceptor offered a 427 with 300, 330, and 400-hp, I suspect the .030 valve lash setting is for the high performance camshaft lift, and not the 300-hp version. In any case, if you are a Chris Craft 427 owner, you would do well to follow their recommendations. Having the valve lash open that far, may be good for high lift cams and high rpm use, but it will make noise. It's better to default to "too open" than "too tight" as the latter will burn valves, and the former is just "noisy".
1966 38' Commander Express
Original 427 power