tuned headers are better than untuned..... and i would see about using a block tester to see if you might be able to retorque the heads...... its a chemical tool you use over your radiator to see if theres any carbon monoxide coming thru.... if there isn't then i would try to retorque but make sure not to loosen and do not go beyond max torque specs..... also check to see if maybe theres a freeze plug that is leaking..... could be something you're not seeing right away.... you could also try using block sealer if you pass the block test...sometimes it works, sometimes it doesn't.... if you do fail a block test.... replace the head gaskets and head bolts.... and check to see if maybe your heads are warped or your block while the heads are off.... use a nice nice flat piece of steel to check.... and i'm sorry but i dont have any torque specs for you... but i'm sure someone else will come along