as far as cutting into the floor board, i used a pair of tin snips from "Harbor Freight" I have 3 different ones "cuts straight" "cuts left" "cuts right" on this particular gig i used "cuts left" and started cutting counter clockwise. Use very small nips 1/2 inch or so and keep the bottom most handle of the tin snips close to the floor, that way there's less of a chance that you will nick a wire. The metal cuts pretty easy, I must have cut around a 11 or 12" diameter hole. Also I did not cut all the way around...I left a tab approximately 3/8" wide to act as a hinge. Use some electical tape on the edges you've already cut while you're working on it....for some reason steel splinters hurt like a mother effer!!!
I started by Checking the fuel level @ the guage cluster...it should read the same when you are done:lol:.........next I disconnected the harness (both of them) and placed them aside..if you have a digital camera it always helps to take pix so you can recreate things and see what goes where.
once you cut your access door the next big job is removing that tabbed retainer ring...the first link shows how I did it but there are other ways.
Interesting to know how you did the diagnosis and how old the replaced pump was..
Mine is pushing 160K; hers is over that now...
DIY and buying acumen are important; a while back, one man picked up an entire fuel tank assembly for $20 !