Butt or lap weld, probably the most debated issue on the autobody forums across the net.
My take is this, there isn't one single butt weld on your truck from the factory, not one single one. There is however lap and pinch welds, EVERY single panel is attached with a lap or pinch weld. This whole floor you are talking about is held in with lap and pinch welds. How on earth could one more be a bad thing?
If you put a lap weld that "looks like it belongs" it will be as good a repair as you can get in my not so humble opinion.
That floor for instance, if you cut the old one off about an inch from the original pinch weld and lay your new piece right up over that strip of the old floor up to the seam from the original pinch weld and plug weld it to the strip, THAT is going to "look like it belongs". If a guy looked at it who didn't know these trucks inside and out he wouldn't even know you did a thing!
No need to fully weld them either, again, there are about four weld beads (short ones) on your whole truck. The rest of the truck is held together with spot welds, thousands of spot welds. A plug weld did with a mig is even better. Soooooo, what in the world is bad about a few more of these type welds?
Make it easy on yourself and do as good a job as they did when they built the darn thing fifty years ago, lap weld it with plug welds.
I replace damaged sheet metal on a weekly basis and I have found the best way to cut a striaght line is to lay a piece of masking tape down and cut along it. Use a 1/32" cut off wheel in a die grinder and run it back and forth a few times thinning the metal alittle THEN start cutting thru.
Brian
