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Well that will toss a bunch of codes
When I monitor my O2 sensors, the 1x1 and 2x1 are constantly changing they other 2 peak and stay steady.
I would say you have a bunch of stuff to sort out, start with secondary and O2 sensors
Then start going over your entire Disco front to back, I think you are going to find a ton of unpleasant surprises.
Plug wires look ancient
I would get an inspection camera with light and pull spark plugs and examine your pistons -look for coolant or steam cleaning
If the pistons are good then you will need to replace the plug wires at the very least as well as the stuff below
You may need coil packs as well
Drain and replace the oil in the Diffs and Transfer case
I would suggest a transmission service
Engine oil change
If you have water in the cylinders or steam cleaning - you need head gaskets at the minimum. it is not hard to do but given that photo you need to ask yourself what else is messed up.
I would say your first step would be to determine if you have any vacuum leaks because of that SAI kluge... Unmetered air entering the intake after the MAF will cause O2 sensors to react.
I agree with @Dave03S you need get the secondary air fixed,but I would start this way :
Pull the spark plugs one at a time use an inspection camera and check for steam cleaning or moisture - hopefully you can rent one. You want try and eliminate a head gasket issue, if everything looks ok then move the steps to that will little bits of money.
In the dark, no lights at if possible. Open the hood start the engine and watch for arcing for the plug wires - those look shot but if you see arcing then that could be part of the misfire issue. We will get to replacing them later.
Fix the secondary air, you need to check the all the vacuum lines, and get that unit re-attached to the head. I can give you some help on that, you will need a 27mm and short 18mm wrench along with some basic tools. You may need to buy some parts.
Then check the O2 sensor wires, disconnect and clean.
Replace the O2 sensors do all 4.
After completing each step other than #1 clear the codes, startup and see if there is any change. This is going to be a bit of a process for you, avoid throwing parts at it.
Secondary air bits -BE VERY GENTLE WITH THE CORRUGATED PIPES THEY TWIST EASILY
The pipes connect to those threaded units in the head. if you do not have them you will need to get at least 2. There are 2 per side. The top was removed on this one, but you can see the corrugated pipes.
