Did you try looking for nuts that have normal and reverse threading for the turnbuckle?
I think everyone here has tried looking for the reverse nuts at one time or another, but they are hard to find locally, without having a machine shop make them. I was going to try backing up the ball cups with smaller PRM plastic nuts (that way the thread wouldn't matter), but there wasn't enough thread exposed to hold it tight enough. The Lunsford Punisher turnbuckles I bought are 1.750", and the FT titanium that it's replacing is 1.585". That's long enough so that when I set-up my car with 2deg. rear toe-in, the turnbuckle is completely threaded into the ball cup. That way it cannot compress. Then the only issue you have is it popping off in a collision. You can solve that with a captured rod end. Right now I have 2 types, a cheep set from Traxxas (for a T-Maxx believe it or not), and a set from GS, which are basically the same. I have reamed out the plastic end for the oversize turnbuckles (1/8" drill bit), but I still have to drill out the captured balls, for the large screws that are required to replace the oversize AE ball studs. I have tried doing this a few different ways, but it's very difficult to do by hand without damaging the ball itself. I will post pics as soon as I have it done.
I wanted to add that the captured balls need to be drilled with a 9/64" bit, so that the proper size screws will go thru smoothly.