Guys,
The front crossbar, along with the dolphin striker and the other two members, form a truss structure.
The front crossbar is a compression member, with almost no bending stress.
There are shear loads at the hulls.
The dolphin striker rod is also compression member (just like mast spreaders)
and the other two members are in tension (just like diamond wires).
A front crossbar, with dolphin striker, does not require a great amount of bending strength.

An I 20 mast section may be too large to fit into the sockets in the P-19 hulls.
I agree that an A Class mast would probably be too thin, that is why I said "an A Class mast and build it up as needed."

Taking an existing carbon mast section and doubling the thickness of the layup is far easier and cheaper than starting from scratch.
The mast section already has a slot for the tramp bolt rope.

Kevin,
That is a good idea to add at least one layer of kevlar.

Basketcase,
A very interesting idea.
We have seen how so much work is involved in removing the mandrel after curing.
If the wet layup were wrapped around a cold metal mandrel, aluminum or steel
, and then heat were blown through the pipe, the pipe would expand tightening the layup
, and heat curing the resin.
Upon cooling(cold water?) the mandrel would contract, freeing itself.