crankshaft spacers

As I reassemble the 948 for the A35, I realized that the freebie crankshaft I
ended up using didn't have one of those thin spacer washers that reside behind
the lower cam gear.  I don't see them listed by the usual suspects, so I
wonder how necessary they are and what their purpose is.  Are they supposed to
perfect the alignment of the timing chain?  If they are really needed, I need
to find a source of one or two of them.

Thanks,
Glen Byrns