Yup, they say a little extra oil cooling with oil flow opposite of water flow.

What size oil lines are you using?

Everything is -10

AN -10 should be more than adequate for what you're doing. 5/8 diameter - good fittings should keep that pretty consistent throughout.

Make sure your fittings are tight AND do not have tension in the hose routing that could make them back-off. They do not need to be "gorilla" tight (you'll gall the threads and the sealing surfaces) but tight enough that they will not back off. And if using push-lock hose, it's recommended to clamp them with a pinch-style clamp (not too tightly either - you do not want the hose's outer casing damaged).

I see you went with non-thermostatically controlled coolers. Depending on their size and given you boat on cooler waters you may find the engines struggle to build oil temp. Buddy ran into that situation running Hardin coolers on 489's both on a nuclear powerplant cooling lake where the water in the summer is 90 + and at LOTO.

Don't cheap out on the AN fittings use Fragola, Earls, Russel ect and don't mix them, match the hose to the fitting manufacturer. personally I think -10 is over kill for your engine

I bought the misc. AN fittings through Hardin and CP. XRP line. These are the only AN fittings that I have so no mix and match other than the way some of them connect. Some are push on, some not.
Thanks for the heads up Tom about over tightening. I've been known to do that. For the oil lines they are the push on style and I did buy the special tool and the clamps for this type of hose.
At the time, I didn't know -10 would be overkill. I think I selected -10 because the Hardin remote oil filter block at the engine was sized for -10. I'm assuming it's not a "bad thing" just overkill and overkill is fine with me.
These coolers are pretty big (overkill) and supposed to work up to 700hp. They are the 3"x23" and they have the power steering loop in them too. I suppose I will find out this spring if they are too big. What is a "desired oil temp" while underway?

I thought you were using compression not push lock, carry on

I don’t think -10 for oil line is overkill at all. IMHO.

Is anyone running one of these or similar? Or was everyone else smart enough to buy their coolers with the thermostat?

Not sure I'm going to have a problem but adding something like this is not a "bad idea" correct? Just momoney and plumbing.....