Don't rule out cutting the gap even bigger, say 3/4" and inserting a filler piece that you can weld on both sides.
in a PERFECT world, your gap should be the size of your welding wire. but sometimes, unless you spend all day getting the perfect patch cut, you're gonna end up with a gap. My experience has been if there is NO gap, it is certianly easyer to weld. But the panel, being smaller in size, will heat and expand at a differant rate then the body panel and warp. A gap will give it room to grow-gonna happen, cant do a thing about it- a lap joint will let it wiggle, but depending on the location, once the car sits outside and the body absorbs the ambiant heat, the lap joint-being twice the thickness of the body metal will heat and expand at a differant rate. and if you sight down the body you'll notice a ripple form along the weld line.. so I would stick to a butt with as small a gap as you can get......... now I know a guy who uses a lap joint and PL 400 adhesive on his own cars with good results
thanks for all the help guys. after much reading and thinking and staring, I went with the filler rod. I measured the gap and it was 1/16" and not an 1/8 which made me feel better. I took a few pics to show how it turned out. i learned a few things from the situation which I am happy to say. First, take your time when it comes to measuring and fitting panels. Second, pick up the gas welder that has been sitting in the corner of my garage for a year and learn how to use it.
I used to hear those story's of guy's butt welding panels together and finishing up with NOT using any Bondo and saying B.S. IMPOSSIBLE. Well even I do it now, butt welding with a MIG sheet metal panels, and not needing anything but a little red spot putty when finished. BARELY needed too. I have NEVER EVER worked in a body shop. If I can do it, ANYONE CAN. COOL DOG EVERETT!!
If I have the room I always come just inside the edge radii and cut if off with a thin wiz wheel then place my spacer pc. inside the factory edge and tack. I know I'm welding 2 areas ( each side of the filler pc.) but that way I'm working on mostly flat surfaces & keep the nice original rolled factory edge. Easier grinding and filling if needed, just the way I do it.
i went and bought one. Have a HF about 1/2 mile from my house so I couldn't resist the price. I think my dog (Dutch) thinks he can drive because he can't get enough of sitting in the driver's seat.
There's alot of misleading information floating around here. If you're wanting some direction about welding sheetmetal..I'd try doing a search, or look at some metalshaping 'based' websites. Max.