I researched oil thermostats and found the Earl's stat to bypass the least amount of oil. The mocal bypasses constantly and every t stat should because a cooler full of cold oil that is suddenly shocked by hot oil could lead to catastrophic consequences. The problem is creates is over cooling. That's where OEM engineering kills it. How big does the cooler need to be, how much air flow, in what conditons? You get the point. It's a guessing game until you throw money and experience at it.
I can tell you now, you will likely need to devise an air shroud for your oil cooler. If I kept Payback, I was going to develop a shroud for daily driving and cool weather driving even with the low flow stat. I found the in radiator oil cooler to be insufficient on the road course only. But, the cooler needed was to big for loping around. Again, engineering...
I'm not sure I would advise a ball valve due to thermal shock. Plumb it and see where the cards fall. If it over cools, build a shroud. If it isn't sufficient, increase the air flow or cooler size.
Good luck....
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Todd
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