It sounds like your 13.5:1 compression is really causing this motor to heat up. I have the same cooling setup as you. I run 90/10 water and coolant with water wetter with a 180 thermo and I have no cooling issues whatsoever. You may need an aluminum radiator.
Also my temp guage went bad once and read way hotter than the car actually was. Make sure this isnt the problem and try what I said above.
Skyler
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-1989 Saleen Mustang #406- TFS Heads, E-303, edelbrock intake,70MM TB, 73mm MAF, off road H, headers and 3chamber flows.
12.55@107mph
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