How is an EFI to Carburetor generally conversion done?

Not a good idea , will fail emission tests if nothing else .

What do you plan to do about an intake manifold for a Holley 350 two barrel.

you want to change an electronic ignition to a mechanical , why !! guess you want more trouble than its worth , leave it , shows how little you know about cars .swap an efi  to an aspirated carby , talk about dumb , what brand of carby .. lol

Engine replacement. You would have to replace or modify far too many parts to make the conversion rational.

The car will not pass modern antipollution regulations as carburetors are not as efficient or run as clean as EFI motors, and use more fuel.  As soon as it is realized your car has been converted back to carburetor likely its registration will be cancelled.

  These modern engines have been designed to run with EFI and it would be a huge mistake to throw all that away and stick a carburetor on in its place.   Also remember you must tell your insurer of any modification made t your car or they can void your insurance if you have an accident, and many car insurers are thrilled to find any unreported modifications as they can refuse to pay for repairs.

That will cause you no end of problems, even if it is made to work. Tell us what problem you have that you think this will fix. Jason, all last  year, you've been struggling with that Jag. Nothing you've tried fixed it so far. Sell it to someone who needs Jag parts and buy yourself a car that runs. An S2000  or Miata could make you happy, if you can find one. At this point your Jaguar is a lost hope, only good for leaving stains in your driveway. Sorry, but the truth really is your friend, though is hurts.

I don't care what you want.  I would never do it.  Just because it won't pass Emissions.  So now it is a piece of junk.

Find an older model of same motor  in a junkyard, swap manifold and .carb(s). . Get on a forum  for your Unknown    year/make/model/displacement  and ask around.

You will have to get a PO box in a non-smog-controlled county to register it (depending, Again, on year, Country.).

I have seen Many go back to carbs. Some get better MPG from 2 well-tuned SUs on a 4 than EFI. I knew a lad with a '67 Malibu, shoehorned a 425  stroker in it that had  feulie  heads; he just charged manifold, put in a Holley 4 bbl.

you'll waste lots of cash on manifolds and distributors lose performance, fuel economy ,never comply to any emission standards if applicable.

Buy or make a manifold and sort out some sort of ignition system most use a distributor and make that fit. but its a silly idea.

Besides that being a more or less stupid idea, it depends on the specific engine and vehicle in question.