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Ok I gave this some thought and I think I understand why the motor is on the pressure side of the pump. It creates a higher pressure zone when picking up heat in the water passages which raises the boiling point. A few psi makes a pretty big difference (Boyle's law). Now the T-stat simply acts like an automated valve. When it opens coolant is sent to the radiators and when closed coolant returns to the water pump for recirculation through the motor.

Frodo,
I like the water jet idea a lot. The pulsing action should help to free anything that got lodged internally. As to pressure, you can get a drip system pressure regulator that will bring your hose pressure down to 15-30psi at any garden center or hardware store. Also use a ball valve so you can control the water flow and ramp it up slowly. I might put a catch screen at the other end and take inventory of everything that comes out. You can count the pieces and see if you got everything.