We used to offset grind 440 steel cranks 30 years ago. It wasn't super expensive back then and it was about the only option that we had. There were a few places that would build stroker cranks by welding and grinding but there weren't any local places that would do it. But that was 30 years ago. I wouldn't even think of offset grinding a steel 440 crank these days much less a cast crank. An offset ground cast crank will probably require a bunch of mallory to balance it unless the bobweight is super low. Seems like an expensive can of worms that could quickly become an expensive pile of junk.