"...If the play on my current pump is not expected it could explain the lack of volume and lower pressure that I'm seeing..."

Good observation. It would be interesting to know just how much "effective" stroke you're actually getting for each cam revolution. It might just be that the internals of that pump are so worn, that it developed too much play to do any good.

If you trust Advance Auto Parts, they list the same pump (Beck Arnley #1515477) for the following:

67-68 122
68-72 142
67-72 144
68-72 145
70-72 164

My hunch is that the spacer was used so that some pump manufacturer could adapt one pump to multiple applications.