Still no start.....What's the issue?
 

After replacing the LS1 block w/ an LS6 block, the engine turns over, but, won't fire. I believe that the PCM is in some type of security mode; even though VATS has been disabled. Is there some Passkey type of program within the PCM that would not allow spark? Also cannot connect OBDII scanner to the PCM.

Initially, the crank sensor had not been connected. Could that have caused the PCM to go into a security mode?

We could really use some help. Thank-you

You really need to scan. Might be cam or crank sensor not working etc.
Try pcm reset. Get the pcm on a bench harness and scan historical codes. If you cant scan the pcm, then it might be dead.

Will do. Thank-you :)