So I spoke with one of my local pool stores that has actual pool guys with years of experience that I trust, we pretty much came to the conclusion that more than likely I don't need a seal plate and to just put on a new diffuser, impeller and shaft seal. I brought all my parts to them when I picked up the new parts and they confirmed my diffuser and impeller were really worn out and more than likely leading to excessive shaft play which was prematurely wearing out the shaft seal. The fit of the new diffuser/impeller is night and day from the old so I think this is going to do it. So far no leaks but time will be the real test. The pump is really pushing now, I can see the water jets really moving the surface of the water more so than they ever have.
As far as the seal plate part number discrepancy goes, they were pretty confident that whenever whoever bought whoever, forgot which company bought who, the PN changed through that process and isn't really relevant in my situation. We did find a little burr from excessive heat on the seal plate where the shaft seal sits flush that may have been contributing also but I decided to just file that flush and see what happens. I don't think it will be an issue tho, gently smoothed it out with a very light abrasive Dremel attachment.
If I remember I'll report back if I have any other issues. thank again for all the help.