Hi Dave
Your car will probably have a catalytic converter with one lambda sensor and also it will more than likely have onboard diagnostics but in a very simple format (OBD1 or flash codes).
The emissions failure may be down to something as simple as an exhaust leak which is drawing air, a perished vaccum hose on the intake or various other issue, not necessarily relating to the catalytic converter.
An exhaust gas readout (4 gases + lambda readings) would narrow down the fault