sometimes I wish I made pics of all the times I have done that to vehicles.
look carefully before you cut. if you can, hack up a junk yard truck with a portable sawzall so you have a good panel and know precisely what you want to do. easy to fawk the lines up if your not careful. but its easy all the way around at that.
I gave up looking for a scrap truck to butcher, so I just made a plate out of sheet steel. Made a gasket out of grey RTV, lined everything with door edge guard. It's a very worthwhile mod, I no longer stress about driving the truck out of town or putting a full tank of fuel in it (the 2 times that fuel pumps always seem to crap out). With the carpet back in, you can't even tell it's there.
Just look closely at Richards pictures and look at your BII. You'll easily see where to cut.
Make a panel like he did, don't try to make a small one just for the sending unit/pump. The other thing in the picture is a vent with a rubber gasket that dries out and leaks gas fumes. You get them both as one part and it's cheap. Replace the hose while you are there, use gas/fuel rated hose or it will fall apart.
Also be sure to replace your lock ring for the sending unit/pump, the old one will flatten out a little and work lose. It has like a double hump and it locks in place. Take it off and put it back and the humps flatten a little and won't stay tight. You'll get gas seeping around the ring if that happens.
BTDT on both of the above, actually a shop resused the old ring and threw away the new ring I gave them and didn't replace the vent and gasket. I had to fix both to stop the gas smell.