Sundance, I too have a '91 V-20 with the orininal
fishbox/pump setup as you discribe. The original pump
looks like a small baitwell pump (not self priming)
and was just barely working when I bought the boat.
I have since bought a Jabsco Water Puppy flexible
rubber impeller (self priming) pump. Since it is self
priming, it can be installed anywhere in the discharge line.
I haven't installed mine yet, I've had some down time over the last several months; I lost my job back in
December, took a new job in January. Four days into the job I fell off a ladder and broke my ankle (needed
surgury to repair). I'm still recovering from that and won't be able to work on the boat until sometime next month. When I do install the pump, I'll let you know how it works out.