Help Finding the Up/Downstream O2 Sensors for my 1996 (Automatic) 2.4 L

I can't seem to source the correct sensors.
What is the deal with the upstream/ Downstream? (Answered below)
Excuse my ignorance.
Recently bought a used 96 with 140k mi Automatic ( 2.4L) 4 Spd


Bone stock.
What has been done:
NGK Iridium Plugs / Wire set (Some oil on the old spark plugs)
Brake rotors/ Drums/shoes /Pads/ Tires
Changed OEM Fuel Filter / Pump
Air Filter
Replaced fluids
Wipers
Cup holders
Fuel door lock (Touch magnet placed)

Needs to be done(for complete tune up/ Peace of mind(Any suggestions?)):

MAF Sensor
O2 Sensors
Distributor
Alternator
Optima/ interstate battery ( Never have let me down)
Rack and pinion
Front Shocks/ Springs

What is missing:
An a/c slider top
Cigarette ash tray
Cooler in the bed full of beers for all of my Tacomaworld buddies.

What is broken/ needs replacing:
Cruise Control, the stalk engages on dash board but does nothing.
Cigarette lighter ( fuse? Cables are bad?)
Exhaust leak. ( haven't found it yet.)
Gear selector is not necessarily sitting in correct position.
Front grille(Bracket where passenger side light has snapped)
ignition/Starter( seems to be sticky/ overcranks by a second)

Error Codes:
P0401 ( Most probably exhaust leak, (replace O2 sensors?) )
P0420 ( most probably due to exhaust leak before Cat)

 

Up stream. Before cat.

 

Understood, does anyone happen to know the respective part numbers?

• just want to ensure it is these
• $53 Denso 234-4154 Toyota 4WD Truck Downstream Oxygen Sensor with 12.9” 4-Wire Harness
  https://www.amazon.com/gp/product/B000C5SG8G/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1
  
• $59 Denso 234-4153 Oxygen Sensor
  https://www.amazon.com/gp/product/B000C5WCRC/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1

 

This help?
https://parts.camelbacktoyota.com/p...&component=&searchText=&startRow=11&maxRow=10

 

Thank you @Babybluetaco for clarifying position of the upstream sensor. & @04TRDV6 for showing me a new source . A Denso rep had emailed me the respective part numbers and they arrive today.

Resources:
I managed to source the parts from amazon and Rockauto.
Amazon.com
Rockauto.com

Parts Locator/ Number Identifier :
Denso Website
http://densoautoparts.com/

 

for the fuel door latch:
if you have access to a 3D printer (or a place that offers this service)
https://www.tacomaworld.com/threads/1st-gen-fuel-door-lock-fix-how-to.330322/

as for the transmission shifter, must be some bushings that are worn out
Here's a video on how to tear it apart and replace bushings
https://www.youtube.com/watch?v=lCY6XyxJjv4

 

@onakat this is awesome! Thank you again for locating the thread for me. I found it way too fun to read and as soon as I have the moment ill get to do it , as per the moment I have a magnet holding the door closed. And I hope that the bushings are the only thing wrong with it (Gear selector). Mind you my gear selector isn't a center selector, it is a stalk coming from the steering column.
I really appreciate you (guys/gals).

 

I just yesterday ordered all 4 bushings for the shifter from @Brice. Quick shipping and included an install video. Should get them on Monday.

 

oh well, then you must look under the dash and follow the lever's mechanism and linkage to see what's loose (probably a bushing somewhere). Don't forget to also look in the engine bay, by the firewall

 

@onakat Will do, I really appreciate it!
@04TRDV6 @Brice I appreciate the reference, I was trying to look into it but did not see a web page link.