So I'm gonna build my own short arms and I was thinking about using Currie johnny joints on both ends. Are there any downsides to that compared to using a johnny joint on one end and a rubber bushing on the other end?

higher cost is about the only drawback

Depending on your control arm angle, you may feel bumps a little more. But that's it

Some say you will feel more vibes from the road with JJ's on both ends, But if it is something you can live with go for it !

I'm running junk rough country x flex arms now so I doubt it could get much worse. I'm gonna build the arms out of 2x2 .25 wall square tubing and go with the johnny joints at both ends. Thanks for the help!!