I had the same water return problem. I bought a copper tee fitting sized to fit the large water return pipe from the rad to the water pump. I also bought several copper reducer bushings and a threaded nipple x mip fitting, and soldered the reducers into the branch of the tee, and tapped the last reducer to match the mip side of the nipple. Then I cut the water hose and clamped the tee in the hose. Do you have the thermostat housing with the water nipple.

Not responsible for advice not taken...