Thanks for all the input, gang.
There seems to be some confusion about how my bobstay is made up. I found an old photo, which you can see at:
which shows the whole thing.
Top to bottom: bronze fitting on sprit, toggle, turnbuckle w/ eye, rod, turnbuckle w/ eye, bronze fitting on boat's bow. You can just make out, near the top, one of the two flat spots on the rod for use with a wrench. You turn the rod to loosen the rig, then pull the clevis pins to disassemble. The top turnbuckle is identical to the bottom one, but in great shape.
Everything looks in good shape except for that cracked bottom turnbuckle, which is all I will replace. I agree that the rod is a different material, and it looks fine.