Shuttle had quite a few variants of the XPC throughout the early-to-mid 2000s and later on. Some of these share components, while others look similar but might as well be worlds apart. This should hopefully help break down some of the differences between types.

Before we begin though, we need to decipher the actual model names, as there is a method to Shuttle's madness, here. For example, let's look at the SB61G2.

The first character (S) is just there for show, in this case it likely just stands for “Shuttle”
The second character (B) denotes the chipset. In this case, B stands for Intel. Here's a quick list of known chipset variants:

• A: AMD (late 2000s)
• B: Intel
• N: Nvidia nForce
• K: VIA
• S: SiS
• T: ATI (Only used for two models, it seems)

It should be noted that the original XPC (the SV-line) do not adhere to this (though it could be argued the V stands for VIA in that case, too).

The third and forth characters are the iteration. In earlier models this just incremented with new models but in later models (such as the SA76G2) it also indicated chipset. (In the SA76's case, it used an AMD 760G chipset. In the SH61R4's case, it uses an Intel H61 chipset, so on and so forth.)
The fifth and sixth characters (G2) denote the chassis and front panel. In the case of the SB61G2 we used as an example earlier, this would mean it's using a G chassis with a front panel used across the G2 line.

In a general sense, chassis components from the same series are compatible with eachother with some difficulty. Notably with the G-series, it was such a long-running chassis that small revisions have been made to it over time to accommodate newer CPUs and components. Those differences will be pointed out in their respective sections.

General Notes:

This is Shuttle's mid-00s bread and butter. I'd wager a vast majority of people who had a Shuttle in this time period had one that was in the G series. It also had a vast collection of accessories (like carrying bags!) made for it.

For the most part, the chassis components are cross compatible. The G chassis has mounting provisions for every type of front panel Shuttle used with this series, both screw posts for the G2 faceplates, or snap-in points for the G5 faceplates.

The only gotcha here is that the front panels have exact port cutouts that may cause problems if you attempt to mix and match front panel components. Pay attention to this as you work. Some of the front panel boards also have different means of connecting to the motherboard (some use the standard headers you'd see in a full size PC, some use a smaller pitch connector, and some use a ribbon cable).

However, in every case observed so far, the front panel essentials (that is, the power button, reset button, and LEDs) all use the standard front panel header connector that you'd see on a full desktop, and most (if not all) Shuttle motherboards have a standard header on board just in case. So worst case, you can connect the buttons and LEDs directly to the motherboard and potentially forego the front panel USB/FireWire/audio.

The ribbon cable style also appears to be cross compatible with other boards and front panels that use it. (Observed moving from SS30G2 board to SA76G2 board in the same chassis.)

Notable tweaks and revisions

Due to being Shuttle's long-running chassis for the 2000s, some small tweaks were made later on to accommodate newer CPUs and such. There are two big ones to watch out for:

Rear exhaust/fan mount: On the newer G-series Shuttles, this was expanded to allow a larger fan and heatsink to be installed, ostensibly due to Prescott Pentium 4s (and their tendency to run toasty). The CPU heatsink mounts are otherwise the same, so you could get away with swapping components here if needed, however the bigger heatsink won't properly bolt up to a smaller rear exhaust. (You can probably get away with this in reverse but it'll look weird.)

CPU cooler mount: On the G-series the CPU cooler (Shuttle's “ICE” system) screws into the chassis, also acting as a means of holding down the motherboard. For the early G chassis, the mount points were fairly consistent, being more toward the rear and centered. Late in the 00s, however, Shuttle moved the CPU closer to the front of the case, and offset it to the right (if looking at the system from the front). These still mate up to the rear exhaust all the same (though they use the larger rear fan mentioned previously).

This is a hypothesis but it seems this may have been to allow the older (and potentially outgoing) G series chassis to share some components with the newer and different chassis types.

NOTE: Page in progress, more added as I can
-xodium