Bruce asked:

I have a 'blad 503CW with the CFE 2.8/80 lens and I would like to get an
adapter for the P series Cokin filters. I think what I need is the "Cokin
Series P Hasselblad B60 Adapter Ring". Can anyone verify that?

That is correct.

You would do better using filters (and adapters) from other manufacturers,
like Lee or Cromatek.
The Cokin thingies aren't exactly the best you can get.

And on a somewhat related topic where does the "B60" designation come from
for the Hasselblad lenses, I measured the bayonet diameter on the 2.8/80
lens and it is something like 64 mm or so depending on where you measure
at. Is this just some kind of "nominal" size?

It is that, more or less.
Derived from, not the size of the mount (which is about 67 mm), but the size
of the filter - the glass bit - itself.