Dang Google. I responded to this but it is unclear whether or not it
posted successfully.

George, I am glad I was able to help you! Unfortunately, since it is
probably too late, I won't be able to use the bed bolt option in
conjunction with the M&T--should have thnked of that when my dad built
it.

Your suggestion to mortise the one piece brings up a couple interesting
questions. First, the bed did not always squeak, that is a fairly
recent thing. It started about a year-and-a-half ago, long after it
was made. My first question is could it be possible that the fact that
he grew like a weed over that time to a solid 5' 9", 180 pound young
man--and still growing and eating and sleeping. I have to wonder if
this doesn't have a part to play in this?

Another question is: Could it be not from the mortise not being deep
enough but from the hardware being pulled, bent, and otherwise
misshapen and stretched? He did rearrange his bedroom all by himself a
few months back and it has been almost unbearable since then. I am
sure he tugged and pulled at the entire bed all at once: headrest,
footrest, side rails, the three LARGE drawers underneath it as well as
the plywood top and the mattress. That could explain the hooks not
fitting tightly...

Thanks for the response!!