I just did this "access panel" thing today (got it done about 4 hours or so ago). I went over to a friend's house in case I needed help (hindsight and all, I probably could have did it at home, but I was kinda glad to do it there).
Anyhow - some suggestions for others who might want to attempt this mod:
1. Loosen the skid plate rear bolts, then remove the front outer bolts and put a couple of long ones in place (same diameter and such - 9/16" - just longer), but snug the nuts up to the same level, then remove the inner two bolts. Then slowly unscrew the outer two to lower the tank/skidplate down (and let it hang). This will give you some extra room to pull the plug (and/or the fuel line if you wish - but I'd leave it on first - no need to spill fuel if you don't have to). When you are done, just reverse the process to snug everything up.
2. Take a piece of steel or aluminium and put it over the the tank/sender location, covering the plug connection, fuel line connect, vapor return hose connection (if you have it), etc. Then, as an extra precaution, put a wet towel over the top of that. I actually used a wet piece of office carpet (my friend has a ton of these squares that we use for all kinds of things).
3. Measure your cut lines, etc - then cut it out; I used a right-angle grinder with a cutting wheel. Wear eye protection (fair warning). I suppose you might be able to use a plasma torch, but it may make too much heat. I would NOT attempt a oxy-acetylene rig. Really, it's such thin steel, a cutting wheel works quick enough. Have a friend and a fire extinguisher around.
4. When done, remove the piece, then remove the wet towel/carpet and the metal plate.
5. Wipe down around the sender unit area (and blow out, etc) any excess dirt, dust, debris, etc - no sense in letting it fall in the tank!
6. To remove the ring, use something that won't spark. I used a foot-long piece of brass all-thread that I picked up at Ace Hardware. Aluminium rod might work as well (I decided on brass because it's a harder metal, and since the lock-ring is steel, it might dig into aluminium - but use what you can).
I used a sender unit from Jeff's Bronco Graveyard. After removing the old sender (which had a completely rotten brass float - which promptly fell into the tank and I had to fish it out with a piece of wire), I found that getting the ring to fit properly was going to be a pain. With the new gasket in place, getting the ring's tabs under the tank tabs was challenging. I ended up taking a pair of pliers and slightly bent the corners of the lock-ring down, so that they would slide easier under the tank tabs. Worked like a charm.
Got everything back together, and once I fueled up - it was a success! All I have left to do now is install some hinges and such, maybe a rubber border (or something to close the gap), and it will be perfect. Right now, I just threw one of those carpet squares over the hole (not a daily driver at all - can't afford the gas!).
Anyhow - I want to thank everyone who posted about their mod here to give me the confidence to try it myself. I didn't catch on fire or blow up; I think if you use some common sense, and put the "shielding" like I did in place (oh - and dropping the tank to move it away from the cutting area), you'll probably not have any problems. Even so, again - keep a fire-extinguisher and friends close by!