I'm not sure if any other case than the 660AV's would fit. Even the Macs using the same case design, the Quadra/Centris 610 and PowerMac 6100, are mismatched in the rear I/O layout. None of the II-series would fit, for sure.
If you're in need of a case, there is one potentially still available on the MLA. It's not pretty, but it's also free (other than shipping costs):