the usual FPdriver is only for the view of all drivers from outside the car ( showroom, replay or other drivers on the track ).
FPDriver refers to First Person Driver which is the arms and legs when in cockpit view and is not the external driver you see from the outside of the vehicle. Just add // to the beginning of the FPDriver entries of the CAS file and you will see that there is no cockpit view driver (arms and legs) but there will be a visible driver in the swingman and other views.
The EXTDRIVERBODY and EXTDRIVERHEAD are the external driver entries.
Also after downloading the mod and looking at the actual CAS files the FPDriver entry is wrong.
The mod creators shouldn't of used the M-FPDRIVER.GMT mesh but rather one of the INT_DRIVER_STYLEXX.GMT meshes for the FPDriver.
In a vehicles CAS file change the FPDriver entry to:
<NOTSPIN><DASHHIGH> MeshFile=int_driver_style01.gmt CollTarget=False HATTarget=False LODIn=(0.0) LODOut=(1.0)
Then for the EXTDRIVERBODY entry change it to:
<NOTSPIN> MeshFile=ext_driver_style01.gmt CollTarget=False HATTarget=False ShadowReceiver=True LODIn=(0.00) LODOut=(230.0)
You can use any Style Number from 01 to 10.
I used Style01 for the Tyrell_002 CAS file driver entries in the image below.
Good Luck