Yeah the inner ball joint are different, but the outside dia of the ball joint unit is the same. The length of the control arm from the inner bj to the outter bj is different, but that needs to be cut anyways.
The XI control arms are perfect for chopping and welding, nice and strong cast iron. Easily machined too should it require it. (Much simpler to modify the bolt it cast piece than fab a tubular arm, but the bonus of tubular is adjustable caster)