I used 1/2 bore, 5/8NF heim joints. The 1 1/4" aluminium round stock is ready made to tap 5/8. I used nuts drilled to 1/2" for spacers. Of course the 12mm bosses are all drilled to 13mm or 1/2". This set up has been on the car for about 3 months now w/o problems. I immediately noticed the increased flexibility and stiffened shifts since the OEM arms are rubber mounted

 

Heim joints typically have low tolerances and wear quickly. The good thing is that a car like the Crossfire has very little suspension travel, so you aren't working the joint very hard, so they should last slightly longer than if they are used in something with more travel.

After they start clunking in a year or so, you can replace them with a variety of other joints. In the rod end world, joints range from Tractor Supply off the shelf heims, to QA1 rod ends to Currie Johnny Joints to really high dollar stuff. The more expensive versions will last longer and are rebuildable. I run Johnny Joints in every suspension link in my Jeep and I'm really happy with how quiet they are and how long they last. They are also pretty cheap and easy to rebuild.

Just some random examples if someone wants to do what you've done and is looking for joints. You can also find a variety of companies that will build the arms for you out of whatever material you want. This is big business in a lot of other automotive circles.

Circle Track Racing Rod Ends | Dirt Track Heim Joints | QA1 Precision Products
Rod Ends - RuffStuff Specialties
Rod Ends
Johnny Joint®

 

What joints are you running? I've never seen one that small.

 

SPRINT CAR 4 LINK 1/2 x 5/8-18 ROD END KIT HEIM JOINTS | eBay

Compared to off road applications, indeed they are small.