hi Bobby,
like james sez, they'll all fit, pick the wire wheels that you like the look of.
But
like 5twins sez XS650s never did have a rear disk wire wheel.
Your easy option is to switch to a drum brake rear.
Your difficult option is to DIY a disk rear by lacing a 16" rim onto a front hub and
following the "front wheel in rear" protocols you'll find by using the "search" button.