Here's some thoughts on fitting PC104 boards into the airframe:
* The internal diameter of the airframe tube is 5.0". * PC104 PCBs are 3.8" x 3.6" x 0.6". Usually, however, the connectors (pin headers) stick out more than that in the plane of the board. We probably don't need any of those connectors, and the ones we do we can replace with vertical ones so let's stick with the given size.
The diagonal on a PC104 PCB is 5.2" so we won't be fitting any in horizontally.
One board will obviously fit if we stick it in vertically. Assuming that the 3.8" side runs vertically, then how many PC104 boards can we stack vertically together in the airframe?
Drawing a rectangle in the circle of the airframe cylinder with the points touching the circle of the cylinder, we can see that the diameter of 5" cuts the rectangle in half (into two triangles). Thus,
a^2 + b^2 = c^2
3.6"^2 + b^2 = 5.0"^2
b = (25 - 12.96)^1/2 = 3.47"
Since each PC104 board is about 0.6" high, we should be able to fit in 5.7 boards -> 5 boards. So I guess we shouldn't be scared about adding 3 if we wanted (586+CAN+PCMCIA).