Chevy motors in Fords?
It does seem kind of dumb in that application. Unless you're talking like LS-series, particularly the newer LS engines, there's just no good reason to go GM over Ford in a Mustang. Ford just doesn't have anything that small, light, efficient, and powerful all in one. (the Modular engines are wide.) Even so it's still sacrilege.
Otherwise, in other cars...non-Fords, cars that never had available V8s and such, well, SBCs are just better supported for non-original applications than are Fords. There's more parts, and more info out there for making them work in cars they were never intended for.
But...putting one in a car that has a well-supported V8 AS ONE OF THE STOCK ENGINES ...is ******* stupid.