3 basics, air fuel spark.
if you have spark and fuel, then its air.

check maf, clean it, check your intake pipe for leaks. how were the o rings on the injector you put in.


if its smoking badly then,
injector, dizzy cap, plug wire, engine harness, and ecu
should NOT be your problem


also, +1 for head gasket, look around the head see if theres any oil stains around head gasket area