You can buy the oil manifold that replaces the cooler from japanparts.
It does have a thermostat integrated.
Since there is no coolant heat exchange, the water pump has one less connection.
You can see the photo of the manifold in my thread.
There still are special rubber couplers (hoses), there are 4 of them, but there is a conduit riser meant to pass under the right side headlight.
Since this was built for a blobeye, the bugeye headlight needs to be modded to allow conduit passage.
My temperatures are quite constant, the OEM size cooler is a good choice for a car that is not tracked all the time.
I have an article in my blog for this.