Cruising miss (lean)

Well, firstly, When cruising or at light throttle accelerating, The engine will want mega-timing; anywhere from 40 to 50 degrees, or more; yes more.
And secondly. the MJs have nothing to do with the cruise fueling unless they are plugged solidly shut!.
>Cruise fueling is handled by the fuel level, the transfer slots and the idle-mixture screws. Cruise fueling is mixed with air from the IAB(IdleAirBleeds) entering the main-wells and emulsifying the fuel that is on it's way to the low-speed delivery ports. It is further smashed into a fine mist by air sneaking past the throttle valves, which you control with the gas pedal.
If the IABs are not emulsifying the fuel, then the fuel drops may become too big to burn in the only-partially air-filled chambers. The fuel just can't find oxygen to react with.
So
the first place to go is the IABs. Then the T-port sync. Then the timing. Later, after this is fixed,you may wish to revisit your MJs. IMO 76s are too big for a typical street cam.

On a different note;
Why did you choose the open-chamber 340 heads for your 360?