You should rough the areas to be epoxied (JB'd) with some coarse paper, file, whatever. Maybe "V" the cutside of the crack just slightly. Clean the living he// out of it with brake cleaner or something similar and let dry. Lay the stuff on, and try to force it into the crack. Probably won't get much in there, but it won't hurt to try. Feather it out over a fairly large area. Pray.
I once repaired a massive crack in the water jacket of a Ford intake manifold with JB. It held for an impressively long time. Cheers, and good luck.