The "Newport" graphics options are the Entry-Level options for the Indy and Indigo 2 series machines. They come with either 8bit or 24bit color and have no dedicated Geometry Engine. So they rely on the main CPU for a lot of graphics applications.
REX3 is the raster engine used on all Newport graphics boards and is the beginning of the graphics pipeline. There is no dedicated geometry engine, so all geometry calculations are done using the floating point unit of the systems processor. All Z buffering is done in the memory of the system.
The "Newport" graphics board for the Indy is just a single board that is plugged on to the Indy mainboard. It houses among other things the REX3 chip and sockets for various extensions. Of course the RAMDAC and the monitor connectors are on this board too.
8bit and 24bit boards look basically the same but the 8bit variants miss some RAM chips so there is empty space an the boards. It is not possible to upgrade from 8bit to 24bit.
The dual head option is a slightly different board than a normal Newport graphics card as the connectors on top of the bottom one installed are in a different position than on the motherboard.
The XL graphics board for the Indigo 2 systems is also a single board that houses the REX3 Raster Engine chip and all other things required by the graphics subsystem. Unlike Newport graphics for the Indy there is no 8 bit version for the Indigo 2.
The XL board fits into the bottom slot of the Indy chassis and connects directly to the motherboard. There are GIO32 slots on top of the graphics board that can be used to install GIO32 options in an Indy (or a dual head card).
In general the Indigo 2 XL board can be placed in any available slot. It is worthy to note though that only one GIO64 device is allowed in each of the GIO64 busses the Indigo 2 offers (each of which may have more than one phyiscal slot). Because of that the choice of position may be determined by other options already installed.