I got a good deal on an ECZ-9425B manifold and I'm in the process of getting it prepped for paint to put it on after smoothing out the venturi holes a little...

Is there something I can soak it in that will get rid of the rust in the thermostat area, as well as any other surface rust as well as the heat riser ports?

Thanks.

The heat riser tube replacement is a 10 minute job with the manifold off.  I used a small punch and carefully knock the old tube out and then use a small hammer to insert the new tube.  Once it is replaced, it should last another 30 years.