Burners are not interchangeable, your air shutter, on burner venturi, should be closed down to around .25" the venturi just slips over the burner orifice, not airtight, your wiring is correct, if the unit was disconnected you probably have air co ing through the pilot and it can take a while to purge, hold a lighter in front of the pilot if the air is purging it will push the flame away from it until fuel is present and it ignites. To be honest with you, from the look of your fireplace, paying an experienced fireplace repair person would be money well spent.