You should be just fine with them that far.
Eddie

Eddie, thanks for your input..matter of fact was going to call you on this...just had not gotten around to it yet...I agree with all you said..figured the silent choice was adding to the issue..was on the boat when I got it...hoping to get it tuned and remove the sensor...mine seems to get killed after a WOT pass and when you shut it down kills it then...idling has been no issue..best we can tell...we are just getting into the EFI deal and my son(in this thread as well) is doing the tuning..we have a drag radial car we race(he drives/tunes) and have gotten a handle on that for the most part and figured time to put our own EFI setup together...getting closer !!

Wonder what kind of setup Merc has on there new line of catalyst motors. They have o2's in the manifolds in the pictures.

you can bet they have it setup with no water until after the cats...

Update for me, no mufflers on the o2 been great. My mufflers where forcing/spraying water back up header hitting sensor.
Ty Skydog

cool...we opened the drain valve under the headers to bleed off some water, and ran with a angled extender, was careful not to chop the throttle after a hard run..but did not kill #3 !!!! still trying to get the tune dialed in...found throttle body was to small...

Any way to tell if the extension on the o2 messed with the reading of the sensor?

seemed slower to read..hard to tell if changed reading for sure....

ok, just installed valves on the water logs, now can bleed off water and I drilled and tapped the Y-pipe to dump the water in, will run with one open, 1 closed and take temp reading one side to the other with a IR gun...see how much this helps...talked to Bob @ marine kinectics and was all in favor of restricting the water...just no idea how much we can get away with...

I bought that 90* adapter/extension and JB welded a piece of brillow pad inside to help keep the water from getting pushed up to the sensor yet it didnt seem to hurt the air flow by just blowing through with my mouth.
So between that and opening up the water drain on the headers, the sensor lived.

The readings seems to react slower than when it was just stuck in the header, but ran into some other issues so I couldnt tell if it read any leaner b/c of the adapter or not.