since i ended up with both early and late ali arms, i thought i would share a pic showing track width differences. i did no measuring and these shots are hardly scientific, but the difference in width comes from the hub. there should be no difference in the length of axles required. spring plate mount is obviously in the same place as well.
here's what they look like (early on top, late on bottom)...
those come from a 924S/86 951 for the early and a 944S/late 951 for the late arm. also, here is a 86 951 rotor on the late arm. goes to show the difference (not i get to order rotors again)...
