Funny that this has come up! I just changed my bilge pump and switch last week.
It was not an easy feat! I have a big block too and the area is very cramped. My switch went bad and the pump was running continuosly last fall (after I hauled the boat) so I simply took out the fuse as a temporary fix to keep the battery alive during storage...This spring when I went to remove the pump I broke the discharge off

The pump gets removed by twisting it out of the base (make sure the hose is off first!) There are three screws in the pump base plate and there are two screws in the switch cover (down the holes

) I was able to reach the screws by hanging upside down and forcing my shoulder down between the riser and floor. It was a major battle all the way.... not in any way easy but certainly doable.
I was going to pull out my back seat so I could atleast lay on the floor and have another 10-12" of reach and that would be my recommendation to you.
I could go into a lot of detail... BTW I replaced my bilge with a 2000 gph Rule pump and switch.
Oh yeah! Remember to dry test the system (dash and switch), wet test (fill bilge with hose) same systems and remember to replace the plug after you drain the last remnants out of the bilge... You can only imagine why I know this
