Check the two hoses for the heater core and be sure both are hot when the engine is warmed up. If they are, then coolant is circulating through the heater core. If not, you may have air trapped in the cooling system from the t-stat/coolant flush and the heater core is the most common place the air settles causing a vapor-lock type situation and no coolant flow through the heater core. These cars have to be bled of air any time the cooling system sis opened using the brass bleeder valve(s) on the t-stat housing and/or coolant transfer pipe near the water pump.
Does the control head switch from floor to vent to defrost? The mode switching is controlled by engine vacuum (as is the cool to hot temperature actuator), so look for cracked/loose/missing vacuum hoses and/or a broken ball shaped vacuum storage canister on the firewall near the brake master cylinder.