Great minds can disagree, and that is certainly the case here. I read about using panel adhesive before doing mine. However, in my opinion (though certainly not an expert), I'd trust a weld first on a structural support, even every few inches. Just my opinion that I'll (hopefully) live with.

 

The welded on cowl panel on an early Mustang is meant to help strengthen the unibody structure to keep the car square and everything in alignment. I don't care WHAT kind of panel adhesive you use, it's not going to be anywhere near strong enough to add any strength to the structure. Do yourself a favor and weld it back in. I'm sure if Ford thought that any kind of glue would do the trick they wouldn't have bothered to spend the time welding it up. It you feel the need to seal the seams, and I'm not saying you shouldn't, you can always use seam sealer on them after you have welded it back on.

 

The technology wasn't there back then, it is there now. If you only did the cowl top it sounds like it would probably be OK, for both top and bottom I wouldn't do it.
As I said the body shop I have used time and time again has claimed they have seen the adhesive hold up a lot better then welds have in accidents.
Lynn

 

I was meaning the top section of the cowl--and those who are make sure to use a good product like 3m.