Sheave's are usually grooved more like this for the wire rope, hard to tell in that picture. Our sheaves were always symmetrical. Also general D to d (sheave diameter to rope diameter) would be 18:1 so that's hugely over sized for what it would need to be, doesn't mean it wouldn't be oversized for another reason.
View attachment 427150
I'm leaning more towards something like this
View attachment 427149
View attachment 427151
You going to Phantom Ranch?