Since the implementation of the STAR smog check program, and the fact that if a smog station loses its STAR certification they'll be losing business, stations are being very careful to ensure that they don't miss anything, most specially, an incorrect catalytic converter or one installed which is not California Air Resources Board certified.
The smog check technician will inspect your Bronco's executive Order (EO) number for the CAT. The EO number should be stamped or printed on the unit and should match the correct catalytic converter EO number for your truck. If the EO number does not match the number which is approved by CARB, the truck will fail the visual portion of the smog check; as an "emissions tamper". Also note, any unidentifiable catalytic converter will cause a vehicle to fail as well.
Special note, this is a visual inspection and the smog technician enters his/her observation into the emission testing equipment (smog machine). What the technician enters determines the outcome of your inspection. It is very possible for a smog technician to not always or always conduct this inspection thoroughly.
Here's some info that might be helpful. Under the new regulation a pre-OBD II (pre-2009) converter can pass the smog check as long as it was installed before 1/1/09 and you can provide the smog station proof of the installation date. If however the installed CAT was not manufactured or approved for installation on your Ford Bronco, it will fail the smog check regardless. The following is a PDF by C.A.R.B. explaining the new California CAT law.
www.smogtips.com/Aftermarket_CAT_ARB.pdf
