I made the change to a Denso a couple years ago. It was more to make sure I didn't get the wrong Walbro then it was for the extra flow..
While my car sat I had no idea the tank rusted up and my existing older pre-problem Walbro pump seized
The vent tube that hangs down and holds the pump is the ground path for the pump. Turns out mine had a cold solder joint and I have no idea how the pump worked right before my car was stolen. Since I had to get the torch out, might as well mod the hell out of it...
http://www.turbobuicks.com/forums/804034-post58.html
NOTE:!!!! DON'T use any of those pics as a how to guide, there's three things you have to do differently! I learned three things after I took that picture.. First the hose clamps are in the wrong place, they have to be rotated so they screws are close to the mounting hose to keep the assy as skinny as possible. Second, the little tit sticking out of the fuel gauge needs to be trimmed down to just above flush with the casing. Those two things will let the fat fat fat pump drop in the tank without having to mess up the O-ring seal.
The other thing you have to do is not assUme GM put the hanger base in the right spot. If you cut the base off and lower the pump you can reach the last 1.8 gallons at the bottom of the tank before you start sucking air and running out of gas (that will apply to a Walboro installation too).
On the electrical side of things, if you run a nice meaty ground lead from the tank/pump to the frame, you have to go up front and run a ground lead from the engine block to the frame. (the car will like it and you'll notice the base FP will jump a few pounds from the ungrounded frame setup)
oh yeah, when you tighten the pump down to the hanger look down in the tank and take note of the baffle. You HAVE to make sure the filter sock is clocked so that the baffle won't curl it upwards. That WILL make you suck air with over 1/4 tank and cause mucho mucho confusion on what's going on with your tune. (ax me how I know!!
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