Please correct me on this if I am wrong but I thought I read somewhere that you could purchase just the friction plate and a hardware kit. The rivets on the stock fly wheel could be drilled out and the friction plate replaced with the new one and hardware?
if you are sticking with a full faced disk, go ahead with the aluminum. If you are using a puck style, on off clutch, save yourself some grief and get the steel.
the friction plate from fidanza doesn't match the stock bolt pattern by the way so dont try and get around it. Do it right the first time get the aluminum flywheel and then you can swap the friction plate for $50. I heard the steel reduces chatter though