You would not want a lower temp thermostat. The D-Jet system already runs the engine rich enough at 75. At anything cooler, it'd be pig rich. You'd probably wash the oil off your cylinders, damaging the engine. 75 is much cooler than modern engines which typically have 90-100C thermostats.

Check out Rialas' pictures - this is why you should have the radiator boiled out, presuming yours is also not a cheaper rebuild (I could have sworn OEM was 3 core but I don't have a 4.5 anymore to be able to check my own. I also don't seem to recall it not taking up the full radiator frame).

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2021 Charger Scat Pack Widebody "Sinabee"
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1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k