smoke after header/head installation - 280z

hey guys,
as for my other post regarding the smoke coming from the engine after my recent head installation, the smoke doesn't seem to be as bad as it was before. but it seems to still be there. i have ran the car several times and changed the old oil and coolant with new fluids.

now i noticed today that when i rev the motor up, while looking at the engine, i can see puffs of black smoke shooting up out of the header/head joint areas around the gasket and it makes me wonder if exhaust is leaking at that area? this brings me to my question... when the header is installed, is it necessary to apply sealant on both sides of the gasket? in this case, the side that butts up against the exhaust ports on the head. i only put sealant around the header flange ports and after it was dry and the gasket on there good, i then attached the header and bolted it down tightly and torqued the bolts. i really don't feel like removing the header again, but i am prepared to do so if my installation was wrong.

thanks in advance,

the bonster