So, with the engine in my shop, I looked at the bell housing and had an idea. I grabbed a Volkswagen engine stand (we build air cooled VW engines at our shop), and held it up to the EA61. Lo and behold, it bolts right up! The EA61 bell housing has the same (or very very similar) dimensions as the old air cooled flat four VW.
So, I got it all set up and started stripping it down. The oil was definitely 45+ years old, I can still smell these pictures.
After pulling the heads, I was pleasantly surprised to see everything was very gross, but in very serviceable shape. The one cylinder that was stuck doesn't have any pits in the cylinder wall, the piston was in poor shape however (more on that later)
Bonus picture of the car after a few rain storms, it is really in good shape overall.
The rear most piston pins were tough to pull, and I don't have any factory tools, so I came up with this little trick. I'd already removed the pistons by the time I took these pictures, so imagine the piston is still in there.
I snuck a narrow 8mm thread nut between the piston and the rear of the block with a magnet, then I screwed a long threaded rod into it (this happens to be a head stud from a VW engine).
I threaded the rod into a slide hammer, and gently hammered the pins out.
After everything was removed, I was left with these super filthy coolant passages to deal with.
Here's the pile of parts after pulling the whole top end. I made sure to keep the liner shims with their corresponding liners, since replacements look to be IMPOSSIBLE to find.