Devices designed for GIO32-bis can be used in GIO64 bus systems.
The Indigo and Indy systems have two GIO slots. The Indigo2 has three physical sockets, but the lower two are paired as a single logical slot--the double socket provides extra electrical and mechanical support for heavy cards. The Indigo2 Maximum Impact has four physical sockets, with each pair ganged as one logical slot. Thus all systems have two GIO slots, electrically speaking.
The form factor depends on the specific platform in which the device is installed. GIO32-bis devices can be either single or double-wide (that is, taking one or two sockets), while GIO64 boards are the size of an EISA board. Slots in Indigo2 systems can accept either an EISA board or a GIO64 board. These two types of boards share common board dimensions but have different connectors for attaching to their respective buses.