Well call me old fashioned but I'm still skeptical!
I have messed around with different epoxies for different uses and they're great. I patched the cracked block in an old Oliver farm tractor probably 10 years ago for my dad. I drilled the ends of the crack, grooved it a little and coated it with epoxy. It's still holding water, and it's survived countless heating/ cooling cycles without cracking or popping off (my big fear).
But I'm still afraid that with the properties the epoxy and steel being different it'll still fail. I think if the materials were up to the task that 3M or PPG or someone would be selling it as a structural repair adhesive now, but they won't take the liability of it failing. Like I said maybe I'm just an old fart but I don't see a no weld solution anytime in the near future.
Old Vettes are a good example- they take a steel frame and mount a fiberglass body on it. But! guess what else is steel- the window frame and the hinge pillars. The firewall is glass, bonded to the steel but they couldn't build them entirely out of plastic. I'm not sure what the latest versions are like, but I'll bet there's still steel in there somewhere.
Here's a good site showing what I'm referring to, (Sorry Mr. Moparts for posting a Chevy link)!
http://www.corvette-restoration.com/restoration/corvette_restoration_updates_all.htmScroll down to the posts from Sept. 2007 and check them out- notice the "birdcage" as he refers to it. It's pretty badly rusted, but he years it all apart and welds in new metal. Now that's the correct repair for repairing the car from a collector's point of view but it also says that even the factory wouldn't use fiberglass for key areas- and that's the exact same area where the crack is on your car!
It might be a hassle to get welding done, unless you can find a trailer and load it up. Take it to a couple shops, show them what you have, ask them for a time and material quote- there are enough small shops around here that do it (and I'm in the boonies). BUt really you're not asking them to fit and repair anything big. That would be cutting back on each side of the crack maybe a half an inch, fitting a patch and welding it in. I can tell from your other work you'd be skilled enough to do the finishing, you could probably even cut out and fit the patch- all they'd have to do is weld it in. And if you find a skilled guiy he might be able to fab a piece to fix the plenum that would make you life easier fixing that.
If you do go with what you've done, keep us posted. Not to be a jerk and say "Told you so", but I'm always looking for stuff that might work. My 69 is going to take some major attention from the AMD catalog to get where you're almost at now, but it's my baby. If it takes me 5 years, OK, so? But other than Fusor for the bottoms of the quarters it's mig time for me!
