Until I remove the corroded material I won't know whether it is actually to the point where the cast is structurally comprimised or not, my point is that if I find it isn't a structural issue the amount of material removed will most likely mean it will benefit from a filler engineered to better withstand the types of loads / stress this type of repair warrants more than bondo, used to cosmetically hide an actual structural repair.
Fortunately, the pitting on my transmission bell housing isn't deep enough to cause any structural issues which is why I decided to use Bondo. After looking up more information about it, Devcon seems very similar to JB Weld, but perhaps a bit stronger.