Two connections - one in and one out.

If you are talking about the one I showed in my original post (same one Rookie is using), yes,it will work on a Gen VI.

I have not used the Earls adapter, but it looks like a nice piece. Might be slightly thinner than the one I used, which would help with filter clearance down in the bilge.

I believe on a Mark 4 you would need the Earl's 504 with the spacer to clear the recess of the oil pad.

That is correct - they show the adapter in the pictures of it.

Is the oil filter line big enough?

Are you talking about the passages in the adapter, or are you asking what size lines to use? I am pretty sure the passages in the adapter should be large enough to not present a restriction. They are larger than what you see with most of the #10 and #12 AN fittings. If you are asking about hose size, someone suggested #12, and I concur, especially if you are making longer runs with your lines. I think I probably used #10, but I only had a total of maybe 18" of line to and from my cooler, and I generally don't run my boat hard for more than a few minutes at a time. As the saying goes, your mileage may vary - if you want to play it safe, go with #12. I'm also running a stock size cooler, which most people will recommend against, but once again I don't run mine hard for more than an occasional short burst. If you like to hold the hammer down for several songs in a row, then probably best to upgrade to a larger cooler. I think what makes it work for me is having the filter right down there on the block and eliminating all the extra hose and restrictive elbows associated with remote oil filters.

Sorry , I ment cooler
Thank you for the info

Is there any reason not to use a thermostatic oil bypass? I'm upgrading my cooling system (again) and was wondering if this is a need to do item. 55*-70* waters, 3x24" cooler, 3/4" -12 lines and ~650hp.

I just my Earls 504 , it a beautiful piece , it's got a thermostat not a bimetallic spring