Hot but Stable - Clutching at Straws

Is the radiator aluminum or copper/brass? If it's the right size for the application it won't matter too much, but an aluminum radiator will cool much more efficiently than a copper/brass of the same size.
What are the dimensions of the radiator?
Rodding out the radiator will help, but there's no way to get it back to 100% efficiency with that method.

Are you SURE the waterpump is the correct unit for the engine?

I would verify the running temp of the engine (perhaps with an IR temp gun) before I did any more troubleshooting. It may not be running hot, but the gauge might be inaccurate.

George