Your pic shows an M71 sherwood pump.
3 stainless bolts hold the impellor housing to the pump body. The heads of the bolts face the bow.
While they are a bit tricky to access, you can get all 3 with an open end wrench.
Remove the bolts & the housing can be wiggled off. Recommend removing the raw water hoses first.
If the impellor is not corroded on the pump shaft, it may come out with the housing.
Notice some gaskets as you dissemble, as they will need to be replaced, Also, it looks like the 'green' around the plate indicates some leakage.
I usually get 800 hrs out of one of these pumps, and replace the impellor as needed, with annual viewing of the impellor. If any vanes are brittle or cracked, out with the old.
usually get 2-300 hrs out of an impellor over 2 seasons.
Anti sieze on the shaft when re-installing a new impellor