Can you do a mechanical DOD delete without the ECM DOD delete?

It will run, but it isn't a finished job. With the AFM hardware removed, the computer is still programmed to use AFM. That usually sets trouble codes and can put the engine in a reduced-power mode.

Short-term workaround (Speedway's suggestion until you can get it tuned): leave the AFM solenoid pack electrically connected — even with a new valley cover you can tuck the original solenoid assembly in the valley or mount it outside — and use a plug-in AFM disabler so the computer never tries to deactivate cylinders. The computer sees what it expects, and the disabler keeps it in V8 mode.

The proper fix is a tune. PCM must be recalibrated to stop commanding deactivation; aftermarket cams also need idle, fuel, spark and torque-model changes. With HP Tuners it's a checkbox to turn AFM off, and since a delete almost always includes a different cam, you'll want a full tune anyway.