Can't be done. The shafts and pulleys are totally different between the two. The AL129x alternator will ONLY work for V-belt engines like the 617 and 117. The good news is that you can easily swap a late MB/OEM 110-150A alternator on to your 603 for cheap. I've done this on several of my 60x engines (and my M119). Details are here:
Installed a 143A alternator in my W124 (86-95 E-class) - with photos
Skip to page 2, post #21, for details on why the AL129x will not work (and why you can't put the late alternator on an old V-belt engine).
