There is a wide variety of turnbuckle styles and configuration.
"Matching" what you have now should be safe enough, but sometimes doing so is difficult if the original manufacturer is out of business.
If you're replacing your turnbuckles then I'd expect (hope) you're changing your standing rigging altogether? Easiest/safest route then is to have a rigger set that up for you.. you can save quite a bit of cash by dropping your own mast, removing the rigging and taking it to the rigger's shop to be replicated all new, including turnbuckles. They can match pin sizes, overall length, size, material and strength (or make recommendations for improvement) If your rigging has stretched over time (noticeable by having very little adjustment remaining on your turnbuckles) they can adjust for that too.