I'm curious if anyone knows of a complete aftermarket IRS system, ie SubFrame and Arms - I'd imagine an aftermarket unit would be lighter and stronger.
There isn't one. Closest would have been the Kenny Brown control arms. But I don't remember the last time I saw those.
You might save some weight with tubular control arms. But I really think most of the weight is in the center section. I remember being surprised how light the cradle was when I had mine stripped down.