I did the repair on my 66 coupe it was not that bad. try to contact this guy (zim64half) he had a different way to do it. I think I would try his way on the next one. It had to do with not cutting out all the welds.
I'm going through this process right now so I'll share my little write-up with you.
Well my solid cowl with just a few pinholes in the hats wasn't as good as I thought.
Here's all I thought I had....
There were some small holes in the top section at the front lip. Seen here: http://webpages.charter.net/jwilson714/Progress/11-9-03/leftcowlfront.jpg
As I was cleaning and investigating how to fix those I notice something on the inside, just underneath the largest hole in that pic. Turns out there was a hole underneath that one in the bottom section. Actually, it runs to almost the center of the cowl as far as I can tell so far.
I bought a 5/16" Cobalt drill bit from Lowe's. It was well worth its $7.50 price tag as I made it through 120 spot welds with one bit (although the last few were difficult). About halfway through the process and after drilling completely through in a couple of places, I decided to take an old high speed steel 5/16" bit that I already had and grind the point down so that it was flat.
This really helped a lot. I used the Cobalt to get started to the point where the hole was just big enough for the flat bit to fit without "walking". I then used the flat bit to cut the weld through the top layer. Worked like a charm but still took about 6 hours to drill out all 130 spot welds (yes I counted them).
This wasn't the end of the work though as I still had to go around with a chisel and seperate the top panel in some places. The top corners ended up pretty mangled due to having several spot welds there which led to very thin metal once they were drilled out.
Yes, that is a washer and 2 nails in there along with another pound of rust particles to go along with the other 2 pounds that I blew out previously. The white stuff you see around the hats is POR putty that I had originally planned to use to fill the pinholes in them.
I made my cut marks on the old metal. Apparently though I was in heat induced stupor and also marked the bottom side of the new panel which led me to making the cut on it instead of the old stuff. *DOH* Luckily I made my cut so that it will be easy to weld back in but that's just more work for me. BE CAREFUL WHERE YOU'RE CUTTING!
I ground all the edges down and straightened them out before applying Bloxide weld-thru primer.
When I got my 69 Mach 1 I looked at the cowl and decided even if it leaked it would be worth buying the car because it was easy to get to, unlike the 68 and earlier cars which had a spot welded cowl panel. If you raise the hood look along the front edge (engine side) of the cowl and you will see a series of screws. These screws when removed will allow removal of the cowl panel, it will still be tight getting in there to weld but at least you don't have to remove the windshield and drill all the spotwelds.
Jpony645 has a nice set of pictures that tell the story. My website does essentially the same, so compare to see the pitfalls I made!
The biggest pitfall for me is only had an old-fashioned oxy-acetelene welder at my disposal (it was/is free to use - right price). This made re-welding the spot welds adversely affect a larger area of the upper cowl. Sealing the cowl when done is the final, essential piece; this shouldn't be forgotten!!
I've done it but haven't updated the website to inlcude pics and description.
Hey im 16 years old and i did it myself, and by the ways its 174 spot welds. It took me around 15 hours to do, and thats under clocking the time. Well have fun, its cool though when that last weld is broke.