Jay,
I second the advice you have already received, but here is another 2 cents: The Lincoln is a great machine, some production shops actually use it. It has plenty of juice for good modulation. That said, welding is really an art. I spent part of my early career as a welder and finisher in a metal fabricating shop and I can tell you that even after 4 years I was still a pedestrian when it came to laying down a really nice weld. TIG/MIG/Stick, it all requires a lot of practice. And the floor panels for our trunks were actually spot welded, if I am not mistaken. You could probably get by with a nicely executed arc weld, but count on plenty of grinding to get things looking smooth. And I would not attempt any of this without removing the gas tank (not that big of a deal).
Practice a bunch on the same guage material until you can put down a bead without burning a hole every few inches!
I envy your ambition, good luck!
g
'64 230sl, fully sorted out...ooops, spoke too soon