Unfortunately the chassis you currently have at hand uses alot of proprietary parts
Getting it to accept other components, like the motherboard(although it is mitx) will require you to mod the backend of the chassis to drop in the add-on motherboard's I/O shield. The other issue is dealing with a proprietary power supply since adding components will require power. Should your PSU go down, it often will mean a particular unit and wattage will go into your X1420 chassis.
Is it possible to pass on your Acer desktop's SKU number in order for us to gauge the system you're currently working off of? We could build you a system of similar stature but with a more higher...