I had one do that to me before. Was so stuck. I was parting out the ski, the Drive shaft was so rusted that the splines wouldn't let go from the prop. I ended up cutting the drive shaft and pulling it off that way. Then I removed the cone from the pump. I used a vice to hold the shaft so I could remove the prop from the pump itself. Then after doing that I took a Drift and hammer and was able to knock the shaft out of the prop. I am telling you all of this so maybe you can try just taking the pump cone off and use a Allen or a big Crescent wrench depending on your pump and unscrew the prop from the pump instead of cutting the drive shaft like I did. This would leave the prop still on the shaft but allow you to get the pump off. Also allowing you to maybe get some PB plaster at those splines to maybe tap the prop off.
Good LUCK
Lube the shaft spline before reassembling will aid in making it easier next time.
