Yes.Yes.
replace the catalytic converter
The catalytic converter(s) would be found in the exhaust system between the engine and the muffler.
It is possible to replace the catalytic converter with a straight-through section of exhaust pipe, but understand that doing so puts you in violation of pollution laws in most states and definitely Federal pollution laws.
Brown and Brown in Mesa Arizona is charging me $1300.00 to replace the catalytic converter and fuel filter.
This would be the sensor after the catalytic converter.
Nowhere. It attached to the exhaust pipe, not the engine.
The bank 1 sensor 2 on a 1996 Chevy Blazer is mounted in the exhaust. Sensor two is just behind the catalytic converter.
There is 1 before and 1 after the catalytic converter.
P0420 = Catalyst Efficiency Below Threshold (Bank1). Sounds like you probably need to replace the Bank 1 (drivers side) Catalytic converter.
how to drai torque converter on 1999 chevy blazer
there are 3 O2 sensors on the 4.3 Vortec V6 Blazer ( I have a 99 as well) 1 is on each exhaust downpipe forward of the catalytic converter, the 3rd is just aft of the converter.