I'm sorry. I thought you were the person who I gave advice on how to repair a 70 coupe cowl vent. I will post a copy here below anyhow. You see, on a 70 coupe, nobdy sells any new metal to replace rusted out cowls. Thus the only fix is to cut something out of a donor car or fabricate your own metal pieces.
I think this proceedure is good however for any type. You be the judge....
Subject: Re: 70 cowl repair
I removed the cowl grill. Then you will see another panel that still covers the cowl pan. If you look closely, this panel can be cut in a few short places and give you good clearance to most areas. I marked the areas to cut, and then drilled a few holes along the outline to use for sheet metal screws to hold it together later for welding when it would be put back together.
I cut along the lines with a saber saw and down the middle of the holes I drilled earlier. After the repairs, temporarily put sheet metal screws into the holes/pieces to hold them in place. After the welding started, the screws were removed as needed after enough welding was started to hold the pieces in place.
The welds are not visible through the grill after the grill is installed.
My cowl was seriously gone also. Major areas were gone completely, but there was enough left to determine the original shape.
I had the complete dash out, metal lower and upper dash pad, and heater box removed along with the windshield wiper motor and arms and engine hood. I laid a wooden platform atop the fenders so I couldl lay across the engine compartment to work on the cowl. Make sure you use good padding under the wood to protect the fender tops.
I then cut thin cardboard, from shoeboxes to form/make the shape of the missing rusted cowl pieces - (I used the cardboard to make a form for the fiberglass). I then taped Saran Wrap to the cardboard - the Saran Wrap kept the epoxy from sticking to the cardboard forms. I then taped the cardboard forms inside or from underneath to the remaining cowl.
I then would apply a thin coat of fiberglass epoxy to the area and then cut small pieces of fiberglass appropriately to lay over the fiberglass epoxy when it became tacky and not fully hard. While still tacky, I would then coat the fiberglass with another coat of epoxy. I repeated this process until I had at least 3 to 4 layers of fiberglass over the missing areas, and 2 or so over areas that remained. I then applied several topcoats of the epoxy over the top of those layers for a final finish.
I then removed the forms from below and painted both from the inside and outside with brush and rattle can as needed. I then cut out the right area and installed the plastic cowl repair caps used to repair earlier model cars. I also used RTV between the cap and the repaired cowl area.
The cowl can essentially never rust out again, and if and what did, doesn't matter, as it is a fully formed epoxy shape. This is what boats are made of. Oh, almost forgot to say, - I used the woven fiberglass and both were the Bondo brand.
2 years later, it is water tight as can be and holding up well. It took a couple of weeks working on it every day and the weekends, but it looks great, and from the outside, you cannot see anything.
There are some who would say to weld in new metal. I like mine now because they are completely fiberglass. In other words, if what’s left of the original metal cowl did rust – it wouldn’t matter. The fiberglass would still be there to keep the rain water out of the car.
Good Luck, and if you decide to do it like me - let me know how it comes out.
I believe this type of repair is the best - it can never rust out again!!!