I got my blowers, cams etc from Dennis r. Extremely low hours as in you almost can't even tell the cams have been run however he said they were set at .020 and show no signs of any wear on the lifters or cams. Personally I typically go by the cam card for known reasons however I will be setting these up as they were. .020. It's gotta be the way the roller rides on the lobe and as we know there differences in lobe profiles. I wouldn't exactly consider that 900 cam to be an endurance cam with the fast opening and closing rates. I would imagine merc knew that and planned on ongoing maintenance but it makes good power also. Some use it in NA engines with excellent results.

I would bet the the majority of the guys buying boats knew with merc SC engines get the majority of their maintenance etc done by merc authorized dealers but I could be wrong.

Valve lash
 

Service manual sets both intake and exhaust at .016 cold

Might be a little trial and error if I use these .016 cold should be around .022 hot. At least from my experience. What heads cme on the 900's? I've got time yet on cams and a lot on my plate at the moment but have a couple other options with cams. I can tame the cam choice/grind down and ease up on valvetrain likely make more power.

Who knows for sure.