I thought I saw a 1/8" stereo jack in one pic but can't be sure. It looks like the perfect way to add pedals to an existing cab.
Depends on which type, how many, and how the pedals are wired.
A 1/8" stereo jack only has three conductors which would work for two microswitch pedals (gas, brake, and ground)
or two analog pedals wired as a single axis
or one analog pedal wired as a dual axis on a single 1/8" stereo jack.

There are more details on single vs. dual axis wiring and which games use which in the driving subforum.
You could fit two dual axis analog pedals
or a microswitch clutch and two single axis analog pedals on a four wire RJ-11. (telephone)
If you need more conductors, you can move up to a D-Sub 9 or an RJ-45. (Ethernet)
Keep in mind that you'll need to have the potentiometers attached to the A-Pac when you boot up the system or it will initialize the 5v + analog input ports as digital buttons.
Scott