I think it was a bit of both IIRC..
the inner bracket pivoted the axle-half and the lower bracket (just at the edge of the chassis)
was fed to an offset bolt or rather an offset bore tube in the chassis for a bolt.
available as stiff offset bore (aluminium?) or
centered bore rubber if you instead wanted a tiny bit of comfort.
I think the plan originally was to help the Lancer torsion chassis' (this one would be one of those btw)
for even more twisting in the frame. (that'D be rubber insert)
Since the "torsion chassis" used rubber grommets to twist the rear end very effectively.
IDK how well that turned out tbh.. but since you don't see that too often these days I'd say not too well
So my best guess would be they then just settled for an offset bore stiff insert to either increase or decrease camber a hair.
There was another kart that had a hidden spring in a hollow chassis tube
for suspension,
but AFAIK that wasn't a Rupp/lancer but a ... uhm....*headscratch*...
Excalibur? sorry.. nope.. can't remember. it was an enduro at least.. side pod tanks and such..
'sid