Partial Floor Pan

Hey everyone -- On a 67 coupe, I'm facing replacement of the left front partial floor pan, possibly the whole left side, and I'm not sure of the best way to stabilize and keep the car perfectly square, level, and untwisted when I cut out the old section. I know my garage floor certainly isn't level. Also, would you recommend weld-through primer between the old & new metal? Lastly, continous weld or spot welds? Any advice would be appreciated.

Great to know, Red5oh. And I visited your cardomain -- what a great car! I may have to do the cowl repair as well, so I'll revisit your site and and look closely at how you did it. I'm just now rolling around the bottom of the car, taking inventory of what needs to be done, discovering busted stuff I wasn't aware of, etc.