I'm missing something, Paul - I don't see why it being a stack pulley keeps it from being pushed further up the shaft. If it has a blind end, that only means you'd have to drill the shaft hole the rest of the way through the pulley and use a grubscrew to retain it axially. I'm not recommending that, without seeing the actual mower, but it's the kind of thing I might do. Never throw away an ill-fitting part if you can make it even worse with an hour's work in the machineshop.