Engine pinging now more like knocking

Valve cover replacement is not going to resolve noises. It would stop oil leakages if there are any.

If the knocking noise is from top of engine, the low oil is the cause of it and topping up the oil might resolve the problem when the hydraulic lifters are pressurised.
If the noise is from bottom of engine and increases in intensity and level with sudden throttle opening, that would be basd news, the con-rod bearings have been damaged by lack of lubrications due the low oil level.