Richard,
I've was out of town on vacation and didn't keep up with this topic until today, but I don't think an oil cooler will help much more then about 5 degrees on the water temp guage. It's my hope that I will see a better benefit in higher oil pressure due to the cooler oil and the increased oil quantity circulating in the system with the cooler and the hoses. In my case my higher then normal temp situation is more related to a currently bad manifold gasket on #6 cylinder (which is making that hole run leaner and hotter, and making the other 5 work harder).
Assuming good water flow through your radiator and engine block, my experience is that over temp is usually related to the engine timing. An oil cooler seems to me to just be a really good simple insurance policy for a 40 year old car more then an active cooling system that will show up on a guage.
Pete