I looked at both locations ans all I found was the letter "A" on the passenger side and on the driver side under the injection pump by the large wire loom was another "A" followed by 30 and the number 2 under the A. All of this was tucked under the wire loom. Is there any other spots to look? I also did not see anything like the crack pictures. But since my truck sepnt 11 years in Wisconsin there is a lot of surface rust on everything underneath but now signs of any track marks.
If you didn't see #53 in the usual spots, you don't have one! Oo.
Have you checked your water pump and radiator for coolant leaks?