Okay, I had a little time this morning, so I went ahead and got working on it. As referenced, the pumps are rated at max 4.5 amps, and the switch max 1.5 amps. So I tried just running both with the existing wiring and breaker. Started by taking out the pump. It is easier if you take the pump out of the housing when you do this, because the wiring is so long, and will get twisted as you unscrew it.
In addition to the valve, you'll need a short 3/4" male-male fitting, easily found at Home Depot in the plumbing section. Screw that into the input end of the valve. You will also need to take the valve apart. Mine used four 5mm internal drive bolts. The reason for that is because as you go to screw it down, the valve body up top will hit stuff.
Looks like this - be careful as the plunger has a spring and it is easy for it to come out, but there aren't any small parts that are easily lost:
So screw the base into the elbow from the tank, then screw the pump's body into the valve. Then rotate it over on its side:
Next comes the wiring. The only tricky part with this is that you need two leads. I decided to run mine at the valve, since the other ends would be water proof, but Y-ing them off would compromise that. I got 6' of marine grade 16AWG cable for htis, but I would have been a little better off with 7', so I'd have an extra 6" for the second lead. Anyway, I wired one long one, and one real short one for hte pump:
Then I connected the water proof connectors previously refernced. Note you can find these on ebay for about $5/pair, which will be easier as it is all in one kit and you don't need to order enough stuff to hit the $20 minimum. Again, Delphi Wather Pack connectors. I put one for the pump on the short lead off of the valve, then routed the other end up to where the pump originally plugged in. If you want to make things cleaner, you can order some extra connectors and cut and splice the one from the pump. I figured I'd just leave it alone, though. Note that everything is wiring in parallel to keep it all at 12V. Also, the valve doesn't really matter which is + and which is -, so long as you runcurrent through it. But I put the + on lead 1 and the - on lead 2 (this assumes that brown is + and black is -........brown is a chassis ground in automotive applications). At any rate, this is what it looks like before I put the cover back on: