Yeah, I've got both JB Weld and Devcon in my garage, and I've always thought of JB weld as just lower end quality Devcon. It's certainly a
lot cheaper.
I got onto Devcon when a mate threw a rod through the block of his V8 car miles from nowhere, and the old mechanic at the little garage out in the sticks had it back up and running sweet in one day, with a new rod, piston and valves, and by patching the hole in the block with Devcon. Like Bill's carb, it was still there, and oiltight, when my friend sold the car a couple of years later.
I've only used it for repairing the engine case on my old GS1000 based drag bike engine, it must have thrown a chain once upon a time, and it didn't bust through into the gearbox like CB750's tend to do, it just smashed off the half of the sprocket cover flange that sits above the sprocket. I just used some plasticine to make a "well" so I could mold the stuff between the engine case and the sprocket cover and dumped it in there, then used a die grinder to shape it once it set, and you wouldn't have known it wasn't OEM. I was even able to drill and tap it for the screws with no problems. Good stuff. Cheers, Terry.