If you want to know if your van has one thats easy, look at the shaft of your key it will have a triangle and two concentric circles on it if its an immobiliser key newer ones also have a 2 to indicate newer code 2 immobiliser system. Of course if you have and older style mechanical pump theres a good chance its been bypassed so you should check the pump to see if the solenoid cover is intact.
Just because they were fitting immobilisers in 1997 doesn't mean your van will have one, they were available simultanously with and without.