10an lines is what I used 515 cu

Tried several brands, never found one that actually worked right.

What are current oil temps? Before or after cooler? That will tell you if the thermostat is needed/important.

i use them on my motors. they work great, my oil temp comes up the 200 degrees and the thermostat opens and my oil temp never moves.

if you don't get water temps up the oil stats wont help, in my personal case I tried with 2 different boats to bring both up, created nothing but work with little to no results. current boat I ran last fal as experiment with oil cooler totally bypsssed and still barely got temps to 200 on the HOT side, that's with no cooler at all, 75 degree lake water with bypasses, for oil stat to get temps up you will need at least 140-150 water temps, I see 110 max. I then figured my boat has been bypasses, no stats and no oil stats since 1987, so I put it the way it came and just go.

I don't remember the brand of oil thermostat I used but controlled oil perfectly it was very similar to the Derale DER-25719 that Summit sells, that may have been the unit.. I ran a 468 ProCharged M3SC and Injected, no thermostat with by pass. Water temp on a hot day with a long run would just break 110 typically stayed in the 100 range, while oil temps would be in the 180 to 200 range. Was running straight W50 Valvoline. This worked perfectly for 6 years before the boat was sold. I understand the current owner is still running the same build and set up today.