Coupla things . . Put a 180° thermostat in it . . 160 is awfully cold for a performance engine.
And, dunno where you're at geographically, but 28° of timing sounds like it might be retarded enough at lower speeds to be heating . . With a Blower motor I'd be running somewhere around 32° minimum total . . . Unless the Distributor is locked out . .
A quick way to check your system and radiator is to take the temp at the thermostat housing and the top of the radiator. Should be within 10-15 degrees of the thermostat temp setting. Then check the temp at the bottom Radiator hose or Tank . . Should be no more than 140°. If it is, either the coolant is flowing through the radiator too fast to be cooled efficiently or you don't have enough radiator . . However, generally, with a standard water pump, this is a condition that shows at speed and at idle or low speed the temp should go down . . just the reverse of your problem.
Another "Dumb" thing to look at is the Water Pump Pulley. Too small and the car heats at speed, too big and it'll heat at low speeds or idle . . Back to water flow through the radiator. Had this problem with a Blown Street Rod . . that's why I'm bald now . . .