I have a similar setup. Setrab cooler in the wheel well. Oil out of the pump housing, to the filter, then the cooler (best to filter the flow before the cooler) and back into the journal on the pulley side of the engine.
I don't have a Mocal sandwich thermostat - because I'm a stubborn curmudgeon - but it's probably better to have one, especially in the midwest.
Even here in balmy California, I drive down into the forties a lot, and in that weather it can take a very long time for the engine to get fully warmed up without the sandwich. I am very careful not to run it hard until the oil is warm, but that can be almost a half-hour sometimes.
In hindsight, this was probably a dumb thing to do. I wanted to keep things as simple as possible, and we were having some space issues fitting the cooler and the filter into the wheel well. But doing dumb things is what these cars are all about, right?
I'd say go with the sandwich.