The bottom rear of the case, with 6-32 threaded standoffs 3/8" high for the motherboard.
3/8" is sufficient clearance for most under-board components, such as Compact Flash.
The PCI slots were tricky..
You should be able to use any 2-slot PCI riser card, as the dimensions are relatively constant.
I chose this Flex Riser:
It's relatively inexpensive, and made by Morex.
Next steps are probably a horizontal support bar going across the middle top of the case - to strengthen the case, and provide a convenient mounting point for the PCI riser, and possibly a vertically mounted 2.5" hard disk.
Other thoughts are to include 1 or 2 3.5" hard disks, and an Opus 120W or similar power supply mounting point off to the left of the motherboard, mounted vertically.