[LS short box]

Couple of other things come to mind.
When you get to the point of plugging in the harness make sure you plug in the crank sensor before you bolt on the starter and exhaust manifold.
Double check your 12 volt feed to the ECM. You will need 12 volt constant and 12 volt in start and run.
The feed wire to the alternator needs to be fairly large. I run a 6 gauge wire from the starter stud to the stud on the alternator.