Here's my solution to factory "ball joints" and "front brakes" on the Cobra ECX 70.
1. Gently remove factory spindles & ball joints:
2. Graft on 250R top a-arms and re-bend bottom a-arms as follows:
The top 250R a-arms slid inside what was left of the Cobra a-arms like they were made fit (diameter wise).
I added +1 to each side while I was at it.
Both sides mocked up:
As a bonus, I can now run 4/144 wheels that all my other quads use.
I'll post pics of the finished product.