My '41 216 had a crack in the water jacket, a little above the rail on the driver's side, about 6 inches long. When the engine was out of the truck, the machine shop cleaned it, "v"ed it, and epoxied it.
Well, guess what, even with the luxury of it being on the work bench, it still leaks.
That's the bad news. The good news is that, as long as it's only in the water jacket, it's not a deal-breaker (in my mind, anyway). The pressure isn't very high in the coolant system, and it leaks intermittently. As long as I keep the level up, no worries.
Anyway, I wouldn't put a lot of faith in epoxying it or JB weld for CURING the leak, but they're easy fixes for at least getting it driveable. Can't speak to welding/brazing etc.
-Hope this helps.
-Michael
