I picked up a MIG welder so that I can get started on my floor pans. My frame is gonna need work too, but I am told to work on the floor pans first before I remove the body, correct?

I am a little confused as what the sequence of steps to follow is. Any help or a web site that details a floor pan install?

I am particularly confused about 'drilling out' the old spot welds. I am not sure where I should be looking for these welds.

Any insight appreciated.

I own a 65, and am in the process of replacing the floor pans, supports and repairing the frame.
I replaced the floor supports. You have to raise the body off of the frame and place 4x4's between the body and the frame to gain access to the welds on the inner rockers. My frame had a dime size hole in the front section behind the front tire. I supported the frame from underneath, cut out the rusted metal, fabricated a new piece (approx same gage) and welded it in.
I am now just finishing the pass. floor pan. I placed the new pan over the old and traced it out.
I adjusted the line I made, so I can perform a lap weld. I cut out the old floor and welded in the new. Now I need to repeat all of this on the drivers side. To find the spot welds, I use a wire brush to clean the metal. You can then notice a dimple of where the spot weld is. Use a spot weld drill bit and grinder to remove them.
Take some time to review all of the past postings for information you need. Once you gain enough confidence, go to it. Be perpaied to do alot of cutting, welding and fabricating.

Thanks. Instead of 4x4, would 2 - 2x2 nailed together and placed on-end work? Should I work think.

I'm not sure of the difference in strength between the two. But I would recomend using the 4x4's. Your car will be resting on these for quite some time and you'll be crawling underneath it also. However a carpenter may have a better answer.

OK, I'll just go with the 4x4