Did you ever find the part for your mast?
I have a Lonestar 16, 1969. I needed a new mast mounting plate (mast step) and mast head. I found the parts at Dwyer Aluminum mast company.
It had all the parts that I needed and can even make a new mast or boom of the same configuration.
The parts are not cheap and it seems like a family owned business. The man and the woman I've reached there seemed like a husband and wife couple. They were not particularly friendly and seemed a bit impatient with my questions, but they had what I needed.
Shipping was prompt.