Lowering brackets for 750's can be had on eBay pretty easily, not sure about 500's. Might want to run a
search here (try "lowering brackets 500" or "lowering blocks 500"), as there are issues with lowering blocks particularly certain designs of them. Shorter shocks are a better solution.
Lengthening the swingarm is possible, but again there are issues. It's all been discussed here at length so use your new friend the
search function (try "extend swingarm" or "extended swingarm" or "lengthen swingarm") and see what people have to say.
mystic_1