https://www.nicoclub.com/service-man...pe/2003/ec.pdf
Go to pages 307 to 313, that is the section that discussing the P0340/345 you're getting.
Few things to check:
1. Fully charge or replace the battery
2. Double check the small ground connections on the top/front of the timing cover (all others ones too)
3. Unplug the cam sensors and see if it starts
Newer vehicles are very sensitive to electrical connections. I replaced a shift cable on my brothers car a few years ago, after install and putting the steering column cover back together car was erratically cranking but no start. I pulled the cover back off, turned out I left a small ground wire unbolted down. Bolted/connected it, car fired right up.

Well that's weird, look on the back of that harness and find the pink wire, that's the one that should be going to your other end on the cam sensor.

See if the wire is loose and pulled out of the harness and is just floating in the air behind it.

EDIT: I'm not expecting you to find a loose wire pulled out, I don't even know how that would be possible on a Nissan harness with it's double lock mechanism to prevent this.

found the pink wire, it’s in pin 114 not 119. Tested and got continuity 0.00. I noticed that after cranking only a couple times that my battery cables are getting very hot, specifically the negative cable. This doesn’t seem right and haven’t ever noticed this before. I have checked and rechecked all ground connections and everything is in place. This is getting incredibly frustrating.

Replace your battery

the battery has been tested for both voltage and cranking amps and tested normal for both but at this point I might as well just in case. I had assumed if the battery tested good… That that not the issue.

Was that a mis-print in the FSM?

Try clearing the codes and using the OEM cam sensors. These cars hate aftermarket cam sensors; OEM or Hitachi are the only reliable replacements.
Since you removed your valve covers, check the electrical connections for all the sub harnesses towards the rear of the engine.

I will try. Can the starter/starter circuit effect this at all?

The only thing that could be a problem (starting related) is the NATS/security system. Maybe try a different key or fob in that case. Otherwise something else isn't right...

well I ran the code reader again... now am getting different code p1065. ECM or ECM ground. But no Cam sensor system codes. I’m really starting to suspect that my ECM is toast.

So, no codes for the cam sensors - but now P1065? Were you able to get the car to start up?
Once again, check all your grounds and electrical connections
Hoping you disconnected the battery when you did all the timing chain related work... if not... oof.

Yes the battery was disconnected during the engine work. I am not a novice when it comes to mechanics. Just semi new to the VQ world. I have been through every ground multiple times and checked for continuity back to the ECM. The engine only cranks and makes absolutely zero attempt at firing. My only conclusion at this point is the ECM itself. And yes for anyone who asks again. I replaced the battery. It did not resolve the issue. As a bit of extra info the engine would still start after the timing went. But after sitting for a few days but BEFORE any work was performed, it behaved the same as it does now.

No longer getting cam angle sensor codes. But DID GET P1065. Which is the ECM or ECM power while ignition is off.
Battery is good.
Cam angle sensor circuit is good.
All grounds have been checked and rechecked.
I AM getting battery voltage at pin 121 on the ECM harness while the ignition is off so the circuit is good.
Engine still makes zero attempts to fire, just cranks and cranks.
I guess it’s the ECM itself?
Hoping to find one locally I can swap in and see if it does it. Anything to look for with that? Are the M/T - A/T ECM the same? I know it has to be the correct year.

When you clear the P1065 code, does it come back up immediately when you try to start it?
I know that the ECU part number MUST match... from there my knowledge is minimal whether it has to be from a MT or AT, but I'd say yes. Pretty sure it has to be paired to the BCM by the dealer.
What are you using at a ground point when you check the voltage at that pin?
@cleric670 maybe you can chime in?

well this is just getting weirder, was just poking around the car and decided to scan again and NOW I’m getting C1136 and U1000 ABS has encountered a problem with the ECU. And the ABS light was flickering and I could hear it clicking in the engine bay and now the car won’t crank at all. Just makes a clicking sound that sounds like it’s coming from the ABS.