Fouled spark plugs

Could you verify the engine, they used 2 v-6 engines in them for the US market, the 3.1 and the 3.8. Both fuel injected. What else does it seem to do besides foul plugs, poor gas mileage or burning oil? Hard starting?

White smoke isn't a good sign. That could be oil or excess fuel. What does it smell like? Does it seem to be using oil? Does the oil smell like gas?

Clogged injectors would lead to a lean condition, not running rich.
How much oil does it go through in 3,000 miles? What has the fuel mileage been doing? As for what to do, I don't know because at the moment we are trying to determine what is actually wrong. I try not to tell folks "Go run this through the engine and change these 6 parts and it will be fine" unless I know those parts are the problem. If the plugs are fouling out, we need to figure out if it's oil, which could mean rebuild or replace the engine due to worn rings or cylinder damage or valve stem seals, or if it's fuel which could be from a bad pressure regulator, internal leakage or high fuel pressure.
If the engine has been running that badly it should also be setting codes, so scanning it to pull those is one thing you could do.

Being a 93 you should be able to pull the codes with a high-tech tool. You need a piece of conductive metal, I used to use a paperclip when out and about. You bridge two terminals and turn the key on and count the light flashes.
https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

If they smell like fuel then it's possible you have an issue with the fuel pressure regulator or the pump, the problem there is that testing requires the engine be running at the time and you will need a fuel pressure test gauge which you can get as a loaner tool from many parts stores. The test gauge gets hooked to the test port on the fuel rail. Then you test the pressure with just turning the key on, then starting and running at an idle and then running at a higher speed. You want to see between 41 and 47 psi of fuel pressure with the key on, then at idle it should be between 3-8 psi lower with the vacuum line attached to the regulator and it should slowly increase as the rpms go up.
The other thing is to pull the regulator vacuum line off and see if there is any fuel in that line. If there is, you need to replace the regulator which on that engine isn't a fun job as you have to remove and take the entire fuel rail apart to replace the regulator block? For that you get the entire unit as a replacement Delco part number 217-3054.

Black throttle body could be from oil or gas as the buildup is from the blowby gases in the combustion chamber and both of those are going to end up there due to the PCV system.

They are not the problem, and they are not part of the head, they are on top and go into the intake manifold. You need to run the tests first and go through the questions I have asked and then we will actually be able to figure out what the problem really is.