1995 Honda Prelude smog test

Before I spend 75 bucks for an assessment and then maybe 300 bucks for a repair that may or may not work, can you tell me what could be the cause why I failed my smog test. I recently bought a 95 Honda Prelude VTEC and the previous owner said he changed out the Catalytic Converter and O2 sensor in April, yet the results show a Gross Polluter and the NO reading was 1952 (max can be 704). It also has a cold air system. Help please.