They stamped over the #s in question then and obliterated the serial # you'd need to give Alumacraft, again I am 100% positive Alumacraft stamped a ser# on the knee brace. Take a green scouring pad to the top flat edge of it, transom to hull bottom, perhaps the #s are hidden by paint drips, dirt or whatever.
KAZ is a state issued #, as noted by GA above
as your user name suggests, I've BTDT, more then once and helped many people figure out old Alumacrafts the way I described, w the # you cant find/see/read.
A well intentioned owner may have deliberately obliterated the Ser# to avoid confusion when the KAZ # was issued.
Alumacraft built some boat models for decades, so determining an exact year is often impossible, even w the correct Ser#, which is why I got a range of years for mine.
As I suggested, send Alumacraft a message and ask them, but I'd bet heavily that they didnt stamp a KAZ # into your boat
State issued HIN tags come as a set of 2. 1 should have been riveted on the top right corner of the exterior transom (which is where they are required to be after 1972) and the other is suggested to be put in a place not likely to been seen unless you go looking for it. Hidden if you will, in case its stolen, a lazy theft might not find and remove it. Both HIN plates are also supposed to be installed permanently, so its obvious if they are removed. IE: w rivets not screws.
So it is HIGHLY likely an owner hand stamped the letters into the knee brace (I have used Harborfreight stamps on more then 1 of my aluminum boats) and then hid the other metal plate under a seat. A swizel head rivet gun can get into some tight spaces, I have used my swivel head to do weird location stuff.
Is the KAZ# on the transom too?
Pix always help too
Did you look thru the FG library GA linked. Not too hard to compare dimensions of what you have to specs and pix posted there to narrow down a model and or range of years.
Not sure what else to suggest, at this point you've gotten lots of good info, from more then 1 source...... sorta feels like :deadhorse:
good luck w your hunt