supposedly the 1.6 has better revvability than the 1.9, and the 1.9 has a better flowing head than the 1.6.
combined, i'm sure the 1.6 could have some mega potential, but the cold starting will suffer.
if everything is good and tight (practically rebuilt motor) it should start like a worn 1.6 in the cold. as long as the GP's are good it shouldn't be a problem. the bigger valves in the 1.9 will really help wake up the motor.
the AAZ alone will produce more torque than the 1.6 + aaz head combo. the 1.6 *may* produce more HP if you mod the pump correctly though (governor)...
i would just stick with the AAZ though... you wouldn't want to mess around with a fresh motor, unless you were seriously hardcore and have some extra money to throw around.
do some searches for malone's franken motor. he had some good results with it, however chrissev tried it and had very poor results.. so much that he got rid of his car and bought a chevy cobalt :? :lol: