Rick,
Not quite the same thing but I have the Mocal SPT-1 thermostatic SANDWICH adapter on my SO, and am having no luck getting
oil up to temp. Bought it from Racers Wholesale and they could only contact B.A.T. in Fla. [US dist.] to find out there's a certain amount of "bleed" past the plunger which must be keeping my temp. from rising to the open point on all but warm days. I wrote a thread about it here months back but got no real fix for problem. Racers said they would replace if it was found defective. Hope your design is not subject to same problem. Pain n a$$ to tear down and lay-up car only to find it's "not defective".
Hope the above leads get you an answer to your question.