How can I tell what ball joint my 2.5" drop spindle uses

[colgad]

I got my 67 C10 truck with 2.5' drop spindles

I do not know what brand they might be.
I do not know where they were purchased.

I would like to know how I can figure out what year ball joint they use

I am buying new A arms and they can come with whatever year Balljoint I need.

The only issue is I do not know which one to choose.
Is there a way to tell?

Thanks so much for any assistance you can give.