I did some digging on the Pontiac PY forum and it seems that some recommend only replacing the seals on the sleeves, so instead of trying to beat on the one that I can't remove, I'll just replace the seal on it.

I''m also going to replace my 11 bolt pump with one that I have seen recommended on this forum by a couple of people
(TFW 43102 11 bolt cast impeller @ NAPA).

I assume that the pump does not include the divider plate. Any recommendations on whether I should get a stainless steel or steel divider plate (I see both available @ Classic Industries)?

As always thanks for the advice. As novice I am learning as I go and the information that's available on this forum has helped me out tremendously and has bailed me out more than once!