You have the whistling BBK throttle body which is what I have, too. Mine whistles when I take my foot off the throttle, though. I've been told that that is the sound of the air rushing through the air bypass valve. Hook up a vacuum gauge to see what your idle vacuum is. Mine, with an E303 cam, is 12" of Hg. You can try to pinch off vacuum lines coming from the intake manifold to see if it rises.
When I'm driving on the highway, my temp stays at about the second notch from the bottom. I have a 180 degree thermostat and that's about what it stays at I would guess. If it's really hot outside and I do a lot of stop and go driving, the needle will go about horizontal.
If you're not using a thermostat at all, expect the temp to rise since you aren't holding the water in the radiator long enough to let it cool off.
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351W 89 Mustang GT Convertible