I didn't know the brake discs varied, I assume they are the same for either system.
I think the caliper is the best way to tell your brake system age. If it has a single piston with crescent shaped pads it is late:
http://www.justkampers.com/shop/type_25 ... right.html" onclick="window.open(this.href);return false;
if it has two pistons with square pads it is early:
http://www.justkampers.com/shop/type_25 ... -left.html" onclick="window.open(this.href);return false;
Gary