60 ft is good.
Oddly, the original has levitate as an SLA and two movement types. Maybe the second movement was swimming, though that sounds weird. Perhaps it can levitate non-flying allies? Or maybe levitate could affect unwilling targets back then, like a minor version of reverse gravity?
CR 6 is ok by me, too.
300 lb?
11-15 HD (Medium), 16-20 HD (Large), 21-30 HD (Huge)? Something a little different?