i wouldnt go with an aluminum one. you just need to set the mesh between the clutch bell and spur gear right and you should be fine. if you get an aluminum one youll probably break some other part of the transmision since you will have way more rotating mass with aluminum.

a good way to set the mesh is to loosen the engine, stick a folded strip of paper between the spur and clutch bell, move the engine so the paper is tight between the gears, tighten the engine down, and take the paper out.