How is the ball joint supposed to attach to that arm? Who makes it? Is it specifically for Fiero, or are you adapting the Caddy suspension? Ask the vendor for specs on those rod ends. Some of them can take a ridiculous amount of load. The skinny ones like those are for high angularity of movement, but I don't see why those are needed in a control arm type of application.
You can replace those with whatever rod end you desire. They are all standardized and available all over the place. Just search for spherical rod ends. There are a bazillion different types, strengths, materials and prices. You can even get rubber or silicone boots for harsh environments. It would be a good idea to educate yourself for your own safety.
1986 SE Aero coupe.
3.4 DOHC swap is complete and running, now just have to finish the rest of the car...
[This message has been edited by tesmith66 (edited 05-25-2014).]