what do you use to cut out floor boards? a grinder or torches or what?

 

I use a cutoff wheel and a sawzall. The sawzall does most the major cutting, but sometimes the cutoff wheel in my rotary grinder needs to be used for hard to reach places.

 

dont use a torch,it will warp the remaining metal and leave you with a lot of grinding,.i used a air cutoff saw withe 3" disc and it worked fine

 

It would also be advisable to remove your gas tank and store it somewhere safe. You're gonna be throwing a lot of sparks around, plus accidentally hitting the gas line can make the car and you go boom!
Also, removing the interior goes without saying....I hope.

 

I use a 4" cutting wheel in my 4" grinder. I have them .032 thick. I like to put the floor in place and cut the new pannel and old pannel at the same time. Here is how the pros do it.

http://v8tvshow.com/content/view/770/1/

 

That's a great video, and definitely the best way to repalce a floor pan, but probably not realistic for most average hobbyists. I sure don't have a rotisserie, nor the room to do one that way.