you might try a 180 deg thermostat. The 160 stat you are using doesn't stand a chance of maintaining a steady engine temp and the wide range of temps you are seeing only make tuning more difficult. A 180 deg stat will narrow the range of engine temps you are see and simplify your tuning efforts. The 180 stat will not make you car run hotter. It will keep it between 185-200 rather than 165-200 like is happening now. It will raise the floor but the ceiling won't change.
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'78 Macho T/A DKM#95, 460cid, SRP pistons, KRE 310 D ports,
3" pypes, Hooker 1 3/4" headers, hydraulic roller,
10" Continental, 3.42 gears
11.5 @117.5mph 3900lbs 
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