How to remove a converter in a stuck assembly

First, I am convinced that the fluid coupler, converter or flywheel was attached to the crank before it was laid in the block. That said, they, at least, made it possible to remove them from an assembled engine, BUT, the crank has to be able to turn. HAS TO.
At the bottom of the starter mounting plate you have a gap that allows you reach up to the nuts with a long 5/8 box-end wrench. Generally, the ratcheting box ends are too bulky…damn it.
You only get a short stroke on the wrench but after a few times a not-too-fat hand can get a finger in there to spin the nut off. I have never found an assembly with rusted nuts/studs; they usually come off easy once loose.
Rotate the crank slightly and repeat 7 more times.

Now, if the crank won’t turn it is most likely rings stuck in the bore and that takes a bit more work. Also, remove the timing chain, no need to spin the cam.
How many ways are there to free up a stuck assembly? This has been covered dozens of times on dozens of threads if you want to search but, here are my thoughts: First, look at all of the bores, above and below the pistons. How much rust? If significant then consider soaking the entire assembly in Citric acid. You will need something 24″ in diameter and at least 24″ tall. Fill with hot water and a couple pounds of the Citric acid, let it sit for a day or two or until the rust is mostly gone. This will also get into the rings and should break that bond. Citric acid will not remove any metal.
No rust? Move to next phase: Spray your favorite ‘stuff’ around each piston top to get lube to the rings. Let soak in a bit.
Choose a rod/piston near bottom of stroke. Remove the rod cap and place short pieces of rubber hose on the rod bolts. Then use a long bar (of some sort) to reach the piston. Try to move the piston/rod up into the bore and remove it. You have now removed, at least, 1/8 of the resistance. Remove all of the pistons that the crank position will allow. Will the crank move now? No? Next phase.
Place a piece of wood 4×4 on a piston top and whack it real good with a 4lb hammer. You are not trying to save the pistons….I hope. Repeat 5-6-7 more times. You are trying to break any bond between rings and cylinder wall.
Any movement? You can repeat the spray lube and 4×4 as many times as you like before the next step.
Obviously, when it starts to move, rock it back and forth until it allows removal of all rods/pistons.
Still stuck? Any of the pistons more likely than another to be the problem?
Do any of your local machine shops still use a hot tank? Ask when they are due to change the caustic solution and ask if they will drop your assembled mess into the tank over the weekend before they recharge the caustic. The caustic will eat through the aluminum pistons, sometimes they will be completely gone depending on the PH of what is in the tank. It will also render the caustic unsuitable for additional use hence the clean-out timing.
No hot tank available? Get out a ½” drill motor and some big drill bits and start drilling through the tops of the pistons, everywhere. Get as close to the cylinder wall as possible but stay behind the rings.
At some point you will be pulling out big chunks and the rod will be (mostly) free. Repeat 5-6-7 more times.
You will win!!