Airbags and ABS were not fitted to European model Fourtrak's, this was for many reasons; the main one being that they are rugged working vehicles, and durably constructed.
Fitting airbags would need a host of electronic circuitry, these would include:
ECU - this would control the deployment and the velocity of deployment according to conditions.
Crash Sensors - these would require fitting on the vehicle, due to their rugged construction Fourtrak's do not have crumple zones, these would normally trigger the sensors as on modern crumple zone equipped vehicles. Sensors would either trigger too soon, or too late rendering them useless.
Speed Sensor - these sense the speed of the vehicle and deploy the airbag at the correct rate and force, more complex sensors include lateral motion sensing, ABS sensing, and dive sensing. These work together to sense the speed, brake force, and the angle of the vehicle to ascertain if it is in danger of rolling and provide the ECU with the correct information to trigger airbags accordingly.
Seat Sensors - these are simple pressure sensors to ensure only airbags on occupied seats are triggered.
Airbag equipped steering wheel and pyrotechnic detonation charge - this is the airbag itself and its explosive charge, this has to be set to trigger at predetermined angles to provide protection for all occupants.
Vehicle occupants could potentially range from large extremely obese adults, to small undersize children, these all have to be accounted for in the airbag's deployment, and its ability to provide protection, rather than injury to these wide ranging occupants.

Being an old design of vehicle it would theoretically be possible to fit airbags, but in reality, too much for a vehicle of such simple design.