Serpent offers a full line of aluminium caster blocks for the Cobra line of cars.
600303 C-hub 10 L+R alu
600304 C-hub 12 L+R alu
600665 C-hub 14 L+R alu
600663 C-hub 16 L+R alu
http://serpent.com/product/600303
Can also be combined with alumnium steerigbblocks #600497
http://serpent.com/product/600497/images/