I have a 73 22-2 and the hull identification number is located on the outside of the transom and is molded in, it's not an aluminum plate. Ppem45 is correct, the tag is the Coast Guard Capacity Plate. As I seem to remember from my last boat, it gives max hp, persons and maximum weight. Last season the local marine patrol did a routine inspection of my boat. They said that it wasn't uncommon for an older hull to have the yellow and black paint worn off of the tag. I asked where I could get it replaced and they said to try and contact Aquasport. (I guess that's not happening)
If I get more information, I'll pass it on. At very least, you now know where your HIN # is.