In reality, the rigging is probably as old as the boat, and so even though the wire looks "as good as new", it may be due for replacement. Given the issues with your turnbuckles I'd say it's time to redo the lot.
Trying to retrofit older turnbuckle sizes/styles is pretty difficult to do unless you can nail down the same supplier - not always possible 30 years on.
Unless you have info that states the rigging's been recently replaced (or replaced at some point) it may well be original, esp since you seem to be dealing with factory hardware.
EDIT: Oops.. sorry - just reread your post and saw that you didn't want to hear this... please disregard!
