I am thinking worse case here. I am hoping not cracked block. If so, wouldnt the oil and coolant mix. I replaced the head gaskets already, but after 3 days of normal driving, the smoke came back. It does it after the car warms up, then seems to go away when driving, but come back at idle. I did have the heads ported but only the exhaust ports.

 

The exhaust porting mighta broken through into the water jacket surrounding it or allowed a very slight crack to form in the exhaust port that starts leaking when it gets hot. That would explain steam out the tailpipes but with no oil/water mixing. It would not explain why new head gaskets would make the problem go away for a while then come back.

Good radiator shops can put a "sniffer" on the radiator and determine if exhaust gasses are being detected in the cooling system- a sure sign that something is cracked/leaking somewhere in the combustion area (cylinder head/block bores/head gasket). They can also pressure test it and see if it holds pressure. If not, it's leaking somewhere, although not necessarily in the combustion space.

 

check your o2's, might have got some rtv or oil on them and they are reading lean. so the ecm is adding fuel and running the engine rich.
i had the same prob. but with a large cam that wouldnt run in closed loop because of the cam overlap. my car smoked white/grey at idle and went away after i reved it up.the o2s read lean ,but the motor was rich.