Hi Again Jeff,
The pumps we use for Tranmission and Differential coolers are pretty expensive, but they don't leak and they are up to the task. For the purposes you have, I am curious why you are not considering using the water pump, itself, as the "pump" to circulate the engine coolant. The port on the water pump itself is the input side - coolant flows into the pump because (rule here) "Water Pumps Suck".. Run your hot side (output from the engine) from the head at back of the intake manifold.
Now - if you are talking about recirculating engine
oil from/to the sump, you will need the high dollar pump or you will have a mess on your hands (and everywhere else).... Fuel pumps will only work for a short time. Once you put 250*
oil through them, the diapraghms and/or shaft seals get hard and crack - leak city....