Air-fuel ratio schooling needed.

70Duster with a 408, mid 90's magnum. Street car, probably will never see the track but I enjoy jumping on it more often than I should. Cam is 235/239 @ .050, 535/550 lift. Stage 2 head porting (whatever that is, didn't get a flow sheet). Not sure what idle timing is at, but total timing is 36btdc. Engine builder (now out of business) said that was best power on the dyno. I put a Holley sniper on it so I now have the ability to fine tune A/f ratio. I have been reading what I can find, but wanted to throw it out here to see what people think.

Right now I have it set at Holley's recommendations other than some enrichment when it's cold. That is idle at 13.5, cruise at 14.7, and wot at 12.5. Other than just randomly changing it and seeing how it acts as I drive it, do these default settings look good and if I was to change it would you go leaner or richer? I hesitate to go much leaner on wot without knowing what I'm doing, but have read 12.8 or so is better with decent flowing heads.

I would try to go as lean as possible with idle, to prevent fouling the plugs.
Lean mixture doesn't hurt anything inside when the engine isn't 'working'.

The 14.7 number is just a "chemical" ratio that means all the air-molecules have burned completely with all the fuel-molecules.
The WOT-number you can only find out (controlled) on a dyno, or on a dragstrip.
The Cruise number, you can try to lean it out for economy until the engine starts to very lightly surge while driving.

Combined with a vacuum gauge and proper ignition curve you can get very good results in tuning the engine.

I'm in the process of tuning my direct port efi right now. I'll preface by saying I'm not an expert, but rather sharing what I have done so far and have had pretty good success.
Idle AFR: Initially it was running around 13.5, but it still smelled like it was running fat. Once I brought it up to around 14.5 it doesn't stink up the garage anymore and it seems to be happy. That being said, I have sequential port injection, not the throttle body style like you. You may have to run it a little fatter but I'd bump it up to around 14 and see how it does. You might even want to try 14.2 range. Does the Sniper system have temperature based enrichment?
As previously mentioned, you should be fine going leaner on cruise RPM. I currently have mine around 15-15.3 for cruise AFR. I think you are fine with the wide open settings right now, but you may be able to go up to 13. In reality, how often will the engine see wide open throttle? Likely for only a few seconds, so it doesn't really matter. If you were running a power adder, I'd definitely recommend keeping it fat up top.
I'm amazed at how clean the plugs and tail pipe are on my car. Almost zero soot in the tailpipe and the plugs look as clean as plugs in a new modern car. It's also nice not smelling like exhaust every time I drive the car.